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Anatomy and Morphology |
Center of Botany, University of Vienna, Rennweg 14, A-1030 Vienna, Austria
Received for publication June 13, 2005. Accepted for publication December 6, 2005.
ABSTRACT
The recent establishment of the new family Calceolariaceae, separated from Scrophulariaceae on the basis of molecular evidence, is complemented here by a scanning electron microscopy study of floral morphology and development of 12 species encompassing all genera (Calceolaria, Jovellana, and Stemotria [= Porodittia]). All species showed a similar pattern of organ initiation. The slightly zygomorphic, four-merous calyx is the first floral organ series initiated, with the primordia emerging consecutively in a unidirectional (dorso-ventral) succession. The two entire corolla lips in Calceolaria and Jovellana arise as uniform meristematic ridges (sometimes with a central emargination, especially in Jovellana), kept apart by two lateral stamen primordia. Later the margins of the lips fuse across the backs of the young stamens, giving rise to the short corolla tube (late sympetaly). Stemotria stands out by having three stamens instead of two and a bilobed lower lip, resulting in a trimerous corolla. Similar architecture was found in teratological flowers of Calceolaria. The perianth of Calceolariaceae is shown to be derived from a tetramerous condition, not from pentamery as traditionally believed. This is in agreement with the separation of Calceolariaceae from Scrophulariaceae and with their placement in succession of Oleaceae and Tetrachondraceae in the basal Lamiales. The hitherto puzzling molecular evidence is thus supported by morphological–developmental features of the flower.
Key Words: Calceolaria • Calceolariaceae • floral development • Jovellana • Lamiales • Stemotria (= Porodittia)
The three genera Calceolaria, Jovellana, and Stemotria (= Porodittia) traditionally have been placed in the family Scrophulariaceae in which they formed a distinct group (ranked as tribe: e.g., Don, 1835
; Bentham, 1846
, 1876
; Wettstein, 1891
; Kränzlin, 1907
; Melchior, 1964
; as subtribe: Lemaire, 1856
; or as subfamily: Luersson, 1882
), but their relationship to other groups has remained unclear. Their position in the Scrophulariaceae depends largely on the definition of that family. Until the advent of molecular systematics, Scrophulariaceae represented a large, morphologically heterogenous group, which had long been thought to be artificial (e.g., Thieret, 1967
; Burtt, 1965
; Hartl, 1955
, 1965–1974
). Recent molecular studies (Olmstead and Reeves, 1995
; Young et al., 1999
; Olmstead et al., 2001
; Oxelman et al., 2005
) definitively proved their polyphyly, and Scrophulariaceae were split into several families. One of these newly established groups was the family Calceolariaceae, comprising the three genera Calceolaria, Jovellana, and Stemotria (= Porodittia) (Olmstead et al., 2001
). Calceolariaceae proved not only unrelated to the other segregates of Scrophulariaceae (e.g., Scrophulariaceae sensu stricto, Plantaginaceae = "Veronicaceae", Stilbaceae), but also placed in a basal position within the Lamiales, preceding the Gesneriaceae and the odd genera Sanango and Peltanthera, and following the Oleaceae and Tetrachondraceae (Albach et al., 2001
; Bremer et al., 2001
, 2002
).
In the present study we investigated how floral morphology and development fit into this picture. While many studies (e.g., Bentham, 1846
; Eichler, 1875
; Wettstein, 1891
; Kränzlin, 1907
; Rendle, 1925
; Lawrence, 1951
; Melchior, 1964
; Vogel, 1974
; Sérsic, 2004
) related the floral morphology of Calceolaria and its allies to that of typical Scrophulariaceae, other authors have pointed out problems in doing so (Schumann, 1890
; Varghese, 1967
; Endress, 1999
). A reinvestigation on a broader scale, that is, one including all genera of Calceolariaceae with an emphasis on floral development, thus seemed necessary.
MATERIALS AND METHODS
The study includes 12 species of Calceolariaceae, covering all genera (Calceolaria, Jovellana, and Stemotria = Porodittia). Inflorescences and floral buds were obtained from field collections (Costa Rica), cultivated plants, and herbarium material. Voucher specimens of field-collected species were deposited at the Herbarium of the University of Vienna, Vienna, Austria (WU).
SEM techniques
Inflorescences were fixed and preserved in 70% ethanol and dehydrated in FDA (formaldehyde dimethyl acetal) (Gerstberger and Leins, 1978
). Herbarium material (Stemotria triandra) was soaked in a 6 : 1 mixture of 10% aqueous aerosol OT (dioctyl sodium sulfosuccinate) and 95% acetone (Peterson et al., 1978
). The specimens prepared for SEM were dissected under a stereomicroscope, critical point dried (Balzers 030 critical point dryer, Balzers AG, Liechtenstein), mounted on stubs with customary nail varnish, and sputter-coated with gold in an argon atmosphere (Balzers sputter coater). The samples were viewed and photographed at 10 and 15 kV in a JEOL (Peabody, Massachusetts, USA) 35-CF scanning electron microscope.
Plant material
The following specimens were used: Calceolaria chelidonioides Kunth, cult. HB Vienna (HBV) (from HB Duisburg (DUIS), no. 742); C. glandulosa Benth., cult. HB Munich (MSB), leg. C. Ehrhart; C. irazuensis Donn. Sm., Costa Rica, Cerro de la Muerte, leg. E. M. Sehr & E. M. Mayr 20040220/01 (WU); C. mexicana Benth., Costa Rica, Cerro de la Muerte, leg. E. M. Sehr & E. M. Mayr 20040220/02 (WU); C. mexicana Benth., cult. HB Vienna (HBV) (from HB Graz (GZU), no. 783); C. nevadensis Standl., cult. HB Munich (MSB), Wei 3659, leg. C. Ehrhart. C. tripartita Ruiz & Pav., cult. HB Vienna (HBV) (from Stuttgart (HOH), no. 1416); C. viscosissima Lindl., cult. HB Munich (MSB), leg. C. Ehrhart; Jovellana punctata Ruiz & Pav., cult. HB Munich (MSB), leg. C. Ehrhart; J. punctata Ruiz & Pav., cult. HB Edinburgh (RBGE), no. 19980699, leg. M. Moeller; J. sinclairii Kraenzl., cult. HB Edinburgh (RGBE), no. 19330356, leg. M. Moeller; J. violacea G. Don, cult. HB Munich (MSB), leg. C. Ehrhart; J. violacea G. Don, HB Edinburgh (RBGE), no. 19684917, leg. M. Moeller; Stemotria triandra Wettst. & Harms, Herbarium HB Chicago (F), Peru, Ancash, Prov. Yungay, leg. Dillon, Molau & Matekaitis.
RESULTS
Floral organography of Calceolaria
The flowers are distinctly zygomorphic, have a four-parted calyx, with the lobes free to the base, and a two-lipped sympetalous corolla. The two stamens, in a transverse position, are fused to a short corolla tube, which encloses the bicarpellate-syncarpous gynoecium. Illustrations of the flowers of many species can be found in Vogel (1974)
, Ehrhart (2000)
, and Sérsic (2004)
.
The four-parted calyx is consistent within the genus. The adaxial calyx lobe is larger than the lateral pair, and the abaxial lobe remains the smallest. Thus, the calyx appears slightly zygomorphic. It is usually green and persistent. The aestivation of the lobes is valvate.
The two-lipped corolla is mostly yellow, rarely white, red, or violet, and often bears markings of variable shape and color (red to purple). The upper and the lower lips are connate at their base and form a short corolla tube. The shape of the corolla is highly variable and can be grouped into several types (Ehrhart, 2000
). The upper lip is usually arched or hooded and much smaller than the pouched lower lip. The majority of species has oil flowers. Their inflated lower lip has an infolded median lobe, bearing a patch of densely arranged oil-secreting trichomes. This "trichome-elaiophore" secretes fatty oil in the mature flower, which is gathered by oil-collecting bees (Tapinotaspis and Centris spp.; Vogel, 1974
). In some species, oil glands are missing and the flowers either offer pollen (but never nectar) to their visitors or are autogamous (Vogel, 1974
).
The stamen pair is placed in episepalous-transversal position. The filaments are inserted at the base of the corolla tube. The anthers are ultimately two-celled, but the cells may be almost completely confluent in some species of sect. Micranthera (Molau, 1988
).
The gynoecium consists of two median, fused carpels, and is superior to semi-inferior (Hartl, 1955
). The style terminates in an inconspicuous or slightly capitate stigma. The fruit is a dry capsule of ovoid-conical shape; dehiscence is septicidal and loculicidal. The capsule bears numerous tiny, striate seeds.
In this study, the floral development of only two species, C. glandulosa and C. viscosissima, is documented in detail. According to Ehrhart (2000)
, both belong to sect. Cheiloncos; C. viscosissima is a member of the C. integrifolia complex (Ehrhart, 2005
). In the other species (C. chelidonioides, C. irazuensis, C. mexicana, C. nevadensis), development does not differ remarkably. In the following descriptions, the adaxial and abaxial side of the flower will be referred to as upper and lower side, respectively.
Floral development of Calceolaria glandulosa
The four-merous calyx is the first floral organ series initiated. The sepal primordia originate unidirectionally in an adaxial to abaxial direction. The upper sepal primordium is first and largest, followed by the two lateral sepals, which emerge more or less simultaneously, and finally the lower sepal primordium arises (Fig. 1a–c).
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The size differences of the sepals are also reflected in the width of insertion. Therefore, the plateau in the center of the floral bud is much narrower on the abaxial side and has a trapezoid form in outline (Fig. 1d, e).
The primordia of the corolla and the androecium arise simultaneously (Figs. 1c–f, 2a). At first, a low circular mound emerges, surrounding a shallow median depression (Fig. 1c).
The two stamen primordia emerge as two ovoid bulges in the radii of the lateral calyx lobes (Fig. 2a). At early stages, they grow comparatively fast, outgrowing the rim-shaped initials of the corolla (Fig. 2b, c). The enlarging stamens rapidly increase in circumference until their margins meet. Thus, they consistently keep the initials of the two corolla lips apart. As growth proceeds, shallow vertical furrows become visible on top of the stamen primordia (Fig. 2d). This marks the beginning of anther differentiation and is quickly followed by the differentiation of a short filament.
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Striking changes in corolla organogenesis occur at later stages of anther differentiation. On the outer surface of the prospective filaments, a meristematic band arises, which connects the margins of the hitherto isolated corolla lips (Fig. 3b), thus forming a short corolla tube (Fig. 3c). The young stamens are enclosed by this newly formed meristematic ring, with their short filaments inserted at the base of the corolla tube (Fig. 3e).
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By the time the lower lip has covered roughly the lower half of the anthers, the upper lip has also enlarged and is nearly the size of the lower lip (Fig. 3e). This process is preceded by the emergence of glandular trichomes on the outer surface of both corolla lips (Fig. 2g).
Shortly after glandular trichomes have started to emerge on the outside of the corolla, the elaiophore becomes visible on the lower corolla lip (Figs. 2h, 3f). In the mature flower, it is represented by a broad band of densely arranged glandular trichomes, which secrete a fatty oil. It is restricted to the central part of the upper border of the lower corolla lip.
Because the elaiophore is formed on the underside of the lower lip, an invagination is required to bring it in its functional position inside the calceolus. Zonal growth of the lower corolla lip results in the required rearrangement. Beneath the prospective trichome-elaiophore, the hairless part of the corolla surface begins to bulge outward. Whereas the upper lip remains relatively short, the lower lip continues to expand and forms a saccate bulge (Fig. 2h, 3f). The enlarging bulge then folds over the band-shaped elaiophore in an upward movement (Fig. 3g). In this (late) stage, the onset of a slight tripartition of the margin of the lower lip can be seen, with the central lobe bearing the elaiophore.
As a result of this enlargement, the median lobe bearing the elaiophore turns and folds into the extended lower lip. Compared to the large, inflated lower corolla lip, the upper lip remains relatively small and is arch-shaped.
The carpel primordia arise as two crescent-shaped ridges. The ridges grow upward and form the incipient ovary walls. The lateral flanks of the carpels broaden until their margins meet and form the septum (Fig. 4a, b). The apex of the young gynoecium tapers during early style formation (Fig. 4c, d). As the prospective style elongates, the terminal slit closes before stigmatic papillae are initiated (Fig. 4d). Finally, the elongating style terminates in a slightly clavate stigma, which comprises numerous papillae (Fig. 4e, f).
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The first noticeable difference between C. glandulosa and C. viscosissima is evident at a later stage of calyx development. After calyx initiation is completed and trichomes have started to emerge from the outer surface, the young calyx lobes enlarge until their margins meet, then they closely curve over the floral apex. Unlike those of C. glandulosa, they cover the developing inner organ primordia completely (Fig. 5a–c).
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In C. viscosissima, many remarkable teratological flowers have been found. One common anomaly observed and documented at various developmental stages is that the lower corolla lip appeared two-parted. The location and depth of this division proved highly variable: the lower lip was either divided into two equal fractions or was asymmetrically cleaved. In some cases, only a slight constriction occurred (Fig. 7a), whereas in others a deep fissure split the lip into two parts (Fig. 7b, c). Frequently, the floral buds with an evenly divided lower lip also developed a third stamen in lower-median position (Fig. 7d, e). In this case, the lip was always deeply incised. After anther differentiation, the orientation of the median stamen could be easily determined; the two regular stamens retained their usual position, the additional stamen was in a median position (Fig. 7f). This is most remarkable, as the floral structure and position of the third stamen is similar in Stemotria triandra (discussed later).
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, Fig. 25F in Wettstein [1891]
, and Fig. 2D in Sérsic [2004]
for J. violacea; Table 5392 in W. Hooker [1863]
for J. punctata; Table 6597 in J. D. Hooker [1882]
for C. sinclairii). The four-parted calyx is similar to that of Calceolaria. The sepals are free to the base, and their aestivation is valvate. Due to their differences in size, the calyx appears slightly zygomorphic.
The two-lipped sympetalous corolla is violet to white or flushed yellow with purple to yellow markings. Both corolla lips are entire, but unlike Calceolaria, protrude forwards and form an oblique bell, with a more or less involute margin. The upper lip is not much smaller than the lower one, but is sometimes shallowly emarginate. The lower corolla lip is never saccate or pouched, and a median lobe (present in Calceolaria and bearing the elaiophore) is absent. Oil-producing trichomes are entirely missing. The flowers are visited by pollen-collecting bees and by oil-collecting bees that gather pollen only (Vogel, 1974
). The lips are connate at their base so that a short corolla tube is formed.
The stamen pair is placed in an episepalous-transversal position. The short filaments are inserted near the base of the short corolla tube. The anther cells are confluent.
The gynoecium is semi-inferior and consists of two median, fused carpels. The style is short and terminates in a capitate stigma. The fruit is a dry capsule of ovoid-conical shape with septicidal and loculicidal dehiscence. The seeds are numerous and striate.
Floral development of Jovellana
The three investigated species (J. punctata, J. sinclairii, J. violacea) are almost identical in their floral development. Apart from minor differences and the fact that oil glands are entirely missing, the floral structure and development are also very similar to those of Calceolaria.
Although we studied the complete floral development in J. punctata, this species tends to produce floral teratologies in cultivation, making interpretation difficult. Therefore, we will first document the essential developmental stages for the calyx in J. sinclairii and for the corolla and androecium in J. violacea, then describe J. punctata.
Jovellana sinclairii
As in Calceolaria, the four calyx lobes emerge consecutively in adaxial to abaxial succession (Fig. 8a–c). Before initiation of the inner floral organs, trichomes emerge from the outer surface of the young sepals. This process starts on the upper calyx lobe and proceeds to the lateral lobes (Fig. 8c–e). The lower calyx lobe is the last one to develop multicellular, eglandular trichomes. The upper and lateral calyx lobes enlarge increasingly, widening to the point where their margins meet. Initially, the lower sepal develops more slowly, but soon catches up (Fig. 8e, f). As development progresses, the calyx lobes bend over the floral apex. Marginal trichomes of the adjacent lobes interlock and seal the calyx in a protective way. Thus, the calyx covers the developing inner organs almost completely (Fig. 8g, h). The calyx re-opens later, after the corolla and androecium are well developed and have acquired their mature shape. Then the previous size differences of the sepals become nearly indiscernible (Fig. 8i).
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After formation of the corolla tube, the upper and lower lips start to bulge over the stamen primordia (Fig. 9g). Unlike Calceolaria, the upper lip grows faster than the lower one. The sinus between the two lips narrows continuously and finally the corolla closes (Fig. 10d, e). The margin of the upper lip slightly overlaps the lower, and glandular trichomes begin to grow out from their outer surface (Figs. 9h, i, 10f, g). Anther differentiation does not start until the corolla lobes overarch the inner organs completely.
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The depression in the center of both corolla lips, observed in J. violacea, proved even more pronounced in J. punctata. Especially in the lower lip, a rather deep fissure formed fairly regularly. In many cases, this feature can also be observed in the anthetic flower, causing a somewhat teratological appearance. Whether this is due to genetic instability of the cultivated material or is in the range of natural variation, is unknown to us. The late development of corolla and androecium is similar to J. violacea.
Organography of Stemotria triandra
The flowers of S. triandra (the only species in the genus Stemotria = Poroditta) differ from those of Calceolaria and Jovellana in the shape of the corolla and the presence of a third stamen. Before going into detail, previous erroneous reports on the orientation of the flower must be discussed. Cavanilles (1799)
was the first to present an illustration of the species (as Jovellana triandra; reproduced in Fig. 11a–a"). His drawing of the flowers is, however, wrong in several respects: the corolla is shown as having two entire, somewhat pouched lips (and thus recalling that of Jovellana), the third stamen is shown in an upper-median position, and all stamens are shown in a transverse orientation. Wettstein (1891)
gave a similar verbal description, apparently based on Cavanille's description and drawings. Kränzlin (1907)
was the first to describe the tripartitioning of the corolla. However, he thought that (as in typical Scrophulariaceae) the two smaller lobes would represent the upper lip and the larger one the lower lip (see Fig. 11b'). Also, Molau (1988)
and E. Fischer (2004)
gave a similar description, but in Molau's illustration the flowers are shown in a reverse orientation (Fig. 11c, c'). In fact, these drawings, which contradict the text, are the only ones that reflect the true orientation of the Stemotria flowers. Our statements are based on photographs kindly provided by Prof. Ulf Molau (Gothenburg, Sweden), herbarium material, and flower development (see the following section). As in Calceolaria and Jovellana (see Weber, 1973
; Andersson and Molau, 1980
), the thyrsic inflorescences are composed of pair-flowered cymes, with each flower pair comprising a terminal and a front flower. Both flowers show equal orientation, with the large corolla lobe pointing upward. Thus, the large median lobe represents the upper lip and the smaller lateral lobes the lower lip. The third stamen occupies a median-lower (abaxial) position (Fig. 12).
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The bright yellow corolla is zygomorphic and sympetalous. The entire upper lip and the bilobate lower lip are never saccate, arched or hooded, but spread patently. The three corolla lobes are almost equal in size, the upper slightly larger than the lower two. The upper and lower corolla lips are connate at their base and form a short corolla tube. Oil-producing trichomes are entirely missing. There are no data on pollination.
The lateral stamen pair is placed in the episepalous-transversal position. The median stamen is abaxial in superposition to the lower calyx lobe. The short filaments are inserted in a distinct, dark purple ring at the base of the corolla tube. Before anthesis, the anthers have a dark, shining, almost metallic appearance. They are two-celled and not confluent.
The gynoecium consists of two median, fused carpels and is surrounded by a short cupular corolla-tube. The conical ovary has numerous densely arranged glands on its outer surface. The style terminates in a pointed stigma. The fruit is a dry capsule of ovoid-conical shape; dehiscence is septicidal and loculicidal. The capsule bears numerous tiny, striate seeds.
Floral development of Stemotria triandra
As in Calceolaria and Jovellana, the four-merous calyx of S. triandra is initiated in adaxial to abaxial succession. Similarly, the adaxial primordium is larger than the lateral pair, while the abaxial primordium remains the smallest. Judging from the prominent glandular trichomes on their outside, the upper and lateral calyx lobes are already well developed when the lower one appears (Fig. 13a). Nonetheless, the size difference of the calyx lobes soon becomes less pronounced (Fig. 13b, c) and is almost indiscernible in the anthetic flower. When the calyx bends over the top of the floral bud, the inner primordia start to emerge.
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In S. triandra, we have observed two teratological floral buds that lack a median stamen. In the first bud, an underdeveloped third stamen primordium was discernible, and two isolated corolla lobes originated at the lower side of the flower (Fig. 13h). In the second bud, which was further developed, the median stamen was entirely missing. As a result, only one lower corolla lobe with a median constriction was developed (Fig. 13i).
DISCUSSION
The flowers of Calceolariceae and historical interpretations
Among the three genera, only the curious flowers of Calceolaria have attracted major attention, and three principal interpretations have been proposed (Note: When referring to penta-, tetra- and dimery of flowers, this relates mainly to the calyx and corolla, occasionally includes the androecium, but does not allude to the gynoecium, which is consistently dimerous in the Lamiales).
1. The flower is derived from a pentamerous condition. In this hypothesis, the lower calyx lobe (the smallest of the four and the last initiated) is interpreted as being formed by two congenitally fused sepals. The upper corolla lip is considered to be the fusion product of two petals and the lower lip of three petals. Of the original five stamens, only two (the upper pair) remain. This view stressing the close relation to traditional Scrophulariaceae is supported by the majority of authors (for references, see introduction).
Vogel (1974)
was the first to recognize the Calceolaria flowers as oil flowers and studied their morphology in greater detail. He regarded the appendage bearing the elaiophore as the median lobe of three congenitally united corolla lobes, but also pondered the possibility that it could be a fusion product of all three abaxial corolla lobes. In both alternatives, the lower corolla lip is regarded as consisting of three petal lobes. Endress (1999)
was the first to study the floral development of a Calceolaria species (C. tripartita) by means of SEM. His statement, "The three petals of the lower lip and the two of the upper lip are completely united and the individual organs can no longer be distinguished" (p. S15), conforms with the pentamery hypothesis. However, he also admitted the possibility of tetramery or dimery. Most recently, Sérsic (2004)
presented a brilliant study of the pollination of Calceolaria. She provided a floral diagram (reproduced in Fig. 14a) showing a tetramerous calyx (said to be derived from pentamery by fusion of the lower sepals, p. 7) and a pentamerous corolla.
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was probably the first to question the presence of a principally five-merous calyx and corolla in Calceolaria. Based on developmental observations, he stated that there was no empirical evidence for a second abaxial calyx lobe and criticized Eichler's idea of a uniform floral organization of Scrophulariaceae. In a study of the floral anatomy of C. pinnata, Varghese (1967)
described the calyx as truly tetramerous and, based on vascularization, regarded the corolla as composed of four petals. His diagram is reproduced in Fig. 14b.
3. The Calceolaria flower is based on dimery. This possibility was recently mentioned by Endress (1999)
. Indeed, from a formal, numerical point of view, the flower could well be composed of two pairs of sepals, one pair of petals, one pair of stamens, and one pair of carpels. Endress, however, did not discuss this interpretation in detail, and left open the question about pentamery, tetramery, and dimery.
Many descriptions of the Calceolaria flower abstain tacitly or explicitly from an interpretation. Bentham (1846
, 1876
), Correns (1891)
, Ritterbusch (1976)
, Molau (1978
, 1988
), Ehrhart (2000)
, and others described the calyx simply as four-parted and the corolla as two-lipped, without referring to their problematic homology.
The flowers of Jovellana have received much less attention and those of Stemotria have mostly been misinterpreted. A discussion, therefore, can be put aside.
Refutation of pentamery
The results of the present study and the critical evaluation of literature data make a derivation from a pentamerous structure unlikely. There are three main counter-arguments:
1. The available developmental data (Schumann, 1890
; Endress, 1999
; this study) give no support for the hypothesis that the calyx of Calceolariaceae is derived from a pentamerous calyx. The abaxial calyx lobe is always initiated as a single primordium. This is in agreement with the fact that none of the three genera and none of the numerous Calceolaria species has a five-merous calyx; it is consistently tetramerous (see Molau, 1978
, 1988
; Ehrhart, 2000
; Sérsic, 2004
). Teratological flowers with five sepals have been described, but in view of the wide range of reported flower anomalies (described in the next counter-argument) evidence from teratology is ambiguous.
2. No evidence is found that the two-lipped corolla is composed of five petals. Three arguments in particular in favor of corolla pentamery need to be discussed. (a) The lower lip is often terminated by three lobes, with the median lobe bearing the elaiophore and folding inward (Vogel, 1974
), thus indicating the presence of three petal lobes. Apart from the fact that some Calcecolaria species do not produce an elaiophore and a median lobe (18% of the species, according to Sérsic, 2004
), this differentiation is an extremely late event in development. The three lobes do not result from individual primordia, but the lower lip is initiated as a single meristematic ridge. Like the upper lip, this occasionally has some bipartition (especially Jovellana), but never a tripartition. (b) Stemotria has a smaller two-lobed upper lip and larger lower lip. This statement is simply based on an incorrect (upside-down) orientation for the flower. It must also be added that teratological flowers of Calceolaria, with divided corolla lips and a third stamen, had a similar structure. (c) Teratological flowers are pentamerous. In Calceolaria, teratologies such as synanthia (monstrous unions of two or more flowers), pelorias, additional stamens, petaloid stamens have been reported repeatedly (Luersson, 1882
; Masters, 1886
; Anonymus, 1874
; Muth, 1899
; Penzig, 1921
; Sérsic, 2004
). Of particular interest are pelorias, which are often considered to reflect ancestral forms in alliances with zygomorphic flowers. Indeed, Masters (1886)
and Muth (1899)
did so when describing and illustrating peloric flowers of Calceolaria species and Jovellana punctata (as Calceolaria punctata) with a pentamerous calyx. Sérsic (2004)
presented a photograph of a flower of C. arachnoidea with a three-lobed lower corolla lip having an elaiophore on each lobe. However, surveying the pelorias and floral anomalies observed so far, pentamery is only one of the numerous variations, and practically any theory of floral origin can be supported by Calceolaria teratologies. In fact, the pelorias of Calceolaria appear to be always terminal. As Hartl (1965–1974)
pointed out for Digitalis, a terminal peloria (in indeterminate inflorescences) must not be interpreted as single flowers showing an atavistic regular floral symmetry, but are in fact synanthia originating from the fusion of several subterminal flower primordia.
3. In Calceolaria and Jovellana, no staminodia are present (or can be detected as vestigial primordia in early development; organ suppression, see Tucker, 1988
), which could be interpreted as remnants of an originally pentamerous androecium. In contrast, the truly pentamerous flowers of Lamiales often produce staminodia when fertile stamens are reduced. This is frequently the case in the Gesneriaceae (Endress, 1998
; Weber, 2004
) and varies to a considerable extent in other families. In Scrophulariaceae s.l., the upper (= median, "odd") staminode is often very prominent and of functional significance (Penstemon, Scrophularia), but may be reduced or completely aborted in other cases. Complete loss of three stamens is rare and mainly found in the tribe Veroniceae. Here, however, the morphology of the whole flower is different (described in Tetramery in Scrophulariaceae). Still more incompatible is the situation when the third stamen of Stemotria (and of teratological Calceolaria) flowers is considered. This stamen occurs in median-lower (abaxial) position and not in median-upper (adaxial) position. Such a position is unparalleled in pentamerous flowers of Lamiales.
Tetramery (or dimery?)
The refutation of pentamery seems to lead automatically to the adoption of tetramery of the flower. The situation is, however, not that easy. The calyx is the only floral whorl in which tetramery seems to be obvious. The corolla and the androecium, however, consist of two elements each: two lips and two stamens. The present results (see also Ritterbusch, 1976
; Endress, 1999
) show that the corolla lips emerge as two transverse meristematic ridges and not in the form of four separate primordia that subsequently fuse. In Calceolaria and Jovellana, there are only two lateral stamen primordia and no vestiges of a median pair. So the idea that the flowers are composed of whorls of two (two sepal whorls and single petal, stamen and carpel whorls in decussate arrangement) appears tempting.
There are, however, arguments against this conception.
1. The sepals are not initiated in two opposite pairs. The observed sequence of initiation can be easily perceived as a unidirectional initiation of a single organ whorl, apparently caused by changes of floral symmetry (see Tucker, 1984a
, b
, 1989a
, 1999
; Endress, 1998
, 1999
).
2. Though the corolla lips do not result from the pairwise fusion of four petal primordia, a slight central emargination of the lip primordia can be often observed (see also Endress, 1999
: Fig. 5i, j). This is particularly obvious in Jovellana (observed in all three species studied), though the lips of the mature flower appear more or less entire. Obviously, we are confronted here with "common primordia" in which fusion of primordia takes place so early that the ancestrally separate initiation can no longer be observed during ontogeny (see, e.g., Tucker, 1975
, 1981
, 1989b
; Gerrath and Posluzny, 1988
; Kirchoff, 1983
; Tucker et. al., 1993
; Endress, 1994
; Caris and Smets, 2004
).
3. Each of the corolla lips receives two lateral vascular bundles, and no median trace is present in either lip (Varghese, 1967
).
4. Flowers with three stamens (Stemotria, teratological Calceolaria flowers) have a deeply incised or emarginate lower lip. There seems to be a correlation of stamen presence and split of the corolla lip. With abortion of the stamen, the split of the lip also disappears. The intimate connection of petals and stamens of C. tripartita (and other "Tubiflorae") has been stressed by Ritterbusch (1976)
, for which he coined the term stamen-petalum complex ("stapet"). The two organs form an intimate unity, and reduction of the one obviously influences strongly the other.
5. Photographs of Stemotria triandra taken by A. Schmidt-Lebuhn (Göttingen) from plants in the wild and in cultivation showed some anomalous flowers, having a tetramerous corolla with a two-parted upper and a similar lower lip. This anomaly might well represent an atavism based on the original tetramery of the flowers.
Tetramery in Scrophulariaceae
Though members of the Scrophulariaceae have fundamentally pentamerous flowers, tetramery is well known in a major group: the tribe Veroniceae. With regard to organ numbers (sepals, petals, stamens, carpels) and the lack of staminodia, their flowers relate well to those of the Calceolaria alliance. The similarity, however, is only superficial. There is ample literature dealing with the morphology and development of the flower of Veroniceae and particular taxa (e.g., Duvau, 1826
; Payer, 1857
; Noll, 1883
; Juel, 1891
; Muth, 1899
; Lehmann, 1918
; J. Fischer, 1920
; Saunders, 1934
; Yamazaki, 1957
; Hartl, 1965–1974;
Hong, 1984
; Lepper, 1984
; Hufford, 1992
, 1995
; Garnock-Jones, 1993
; Kampny et al., 1993
, 1994
; Kampny, 1995
; Kampny and Dengler, 1997
; Fischer, 2004
), paralleled by recent molecular studies (see Albach et al., 2004a
, b
, 2005
, and references therein). The following statements are generally accepted:
1. In Veroniceae, the widespread tetramery of the calyx is due to reduction of the uppermost (median) sepal. All conceivable transitions from a normal presence to diminution to complete loss are represented, leaving no doubt that calyx tetramery in particular species or genera is a phylogenetically derived condition. As always, the uppermost sepal is reduced and the four remaining are placed in a diagonal position, while those of Calceolariaceae are arranged orthogonally.
2. The undivided upper lobe of the flower of the core Veroniceae (Veronicastrum, Veronica, Hebe, and allies, Derwentia and Synthyris) is made up of two fused petals and thus corresponds to the upper lip of other Scrophulariaceae, while the two lateral lobes together with the lower lobe represent the lower lip. Evidence is derived from the comparison with related genera (Wulfenia, Picrorhiza, and Neopicrorhiza, with a bilobed upper lobe, Paederota with an either one- or bipartite upper lobe), vascularization (upper lobe often with two "midribs" and symmetrical bundle arrangement), and teratology (flowers often completely five-merous). Regarding development, however, it must be noted that in (all?) Veronica species the upper lobe is initiated as a single ("common") primordium. Nonetheless, no author has taken this as an indication for true tetramery of the corolla. Two separate primordia or an emarginate meristematic ridge may occur in Paederota, but data are lacking so far.
The four corolla lobes of typical Veroniceae are thus arranged in an orthogonal cross, while they are in diagonal position in Calceolariaceae.
3. Though typical Veroniceae have two stamens and lack staminodia, there are ancestral genera with four stamens (Picrorhiza, Neopicrorhiza).
In summary, the flower of Veroniceae can be well derived from the pentamerous structure of other Scrophulariaceae, and its structure differs strongly from that of Calceoariaceae. A phylogentic relationship of the two groups, therefore, cannot be assumed and, in fact, has never been taken into serious consideration.
Tetramery in Lamiales
Within the Lamiales, only two families are characterized by flowers with an almost exclusively tetramerous perianth: Oleaceae and Tetrachondraceae. The morphology and floral development of these families was investigated in a parallel study by E. Sehr and A. Weber (University of Vienna; unpublished data). The flowers of both are radially symmetric (at least as far as the perianth is concerned), but differ in the position of the sepals and petals and the number of stamens. In the Tetrachondraceae (two genera, three species), the sepals are initiated in diagonal and the petals in orthogonal position, and four stamens are present. In the Oleaceae, the sepals are initiated in orthogonal position and the petals in diagonal position (except Nyctanthes and Jasminum, in which the arrangement is somewhat irregular due to the five- to eight-mery of the flowers) and usually only two stamens (in transversal position) are formed. The flowers of Oleaceae thus agree remarkably with those of Calceolaria and Jovellana. One could even say that the flowers of these genera are oleaceous flowers strongly overformed by zygomorphy. Apart from the unidirectional development of the calyx, a major difference is the presence of four separate petal primordia in Oleaceae. The occurrence of four stamens in Oleaceae has been reported for several genera (Weber, 1928
; Melchior, 1964
; Wallander and Albert, 2000
; Green, 2004
). However, all belong to tribe Oleae and thus to a rather advanced group of the family (Wallander and Albert, 2000
). It is, therefore, uncertain whether this can be regarded as an ancestral condition or a secondary (re-)acquisition. No data are presently available on whether the median stamen pair is initiated synchronously or later than the lateral pair.
When speaking of flower tetramery in Oleaceae, Tetrachondraceae, and Calceolariaceae, this only refers to the condition observed in the extant members of these families and says nothing about the origin and the ancestral condition. In fact, arguments have been proposed that the oleaceous flower is based on dimery (Torgård, 1924
; Weber, 1928
). However, no support has been found in our developmental studies (E. Sehr and A. Weber, unpublished data). It is also hardly conceivable that the undivided corolla lips of Calceolaria and Jovellana represent a more ancestral condition than found in Oleaceae.
Position of Calceolariaceae in the Lamiales
Even from a strictly morphological point of view, a placement of the Calceolaria alliance within Scrophulariaceae appears no longer tenable. An inclusion into Gesneriaceae, with which Calceolariaceae share the peculiar type of thyrsic inflorescences with pair-flowered cymes (Weber,1973
, 1982
; Andersson and Molau, 1980
) and similar seeds (aulacospermous, endothelial cells in longitudinal rows and causing longitudinal furrows in the ripe endosperm; Hartl [1965–1974]
; A. Weber, personal observations) can also be ruled out because of principal pentamery of the Gesneriaceae flowers (Weber, 2004
). The only sound association is with Oleaceae and Tetrachondraceae, and this is exactly what molecular systematics indicates: Oleaceae represent one of the basalmost families of Lamiales, only preceded by Plocospermataceae and (possibly) Carlemanniaceae, and followed by Tetrachondraceae and Calceolariaceae. Peltanthera, Sanango, and Gesneriaceae then form a group with pentamerous flowers and are sister to the "higher" Lamiales, which comprise the Scrophulariaceae, Plantaginaceae, Stilbaceae, Bignoniaceae, Acanthaceae, etc. (Oxelman et al., 1999
; Savolainen et al., 2000
; Albach et al., 2001
; Bremer et al., 2001
, 2002
; Olmstead et al., 2001
; Andersson, 2003
). The molecular evidence thus can be well paralleled and substantiated by floral morphology and development. This is considered a significant prerequisite for a future multidisciplinary character evaluation and cladistic analysis of the basal families of Lamiales in order to assess their phylogenetic relationships more accurately.
Relation between Calceolaria, Jovellana, and Stemotria
From the viewpoint of floral morphology, the three genera are well characterized and taxonomically separable. Jovellana and Calceolaria indeed placed as sister groups in the molecular study of Andersson (2003)
. As indicated by floral morphology, Jovellana is definitely more primitive than Calceolaria (simple structure of the corolla lips, lack of an elaiophore). One would expect the same for Stemotria (simple corolla structure, the third stamen being possibly an atavism). In the molecular tree, however, this genus proved to nest in Calceolaria. This unexpected result needs confirmation. Nonetheless, in view of the developmental similarity of Stemotria with three-staminate teratological flowers of Calceolaria, the idea that Stemotria (comprising only a single species with narrow distribution) is only a genetically fixed teratology of Calceolaria, does not seem absurd.
|
1 The authors thank Dr. C. Ehrhart (University of Munich, Germany), Dr. M. Moeller (Royal Botanic Garden Edinburgh, UK), Prof. Dr. U. Molau (Gothenburg, Sweden) and Dipl. Biol. A. Schmidt-Lebuhn (University of Göttingen, Germany) for providing fixed material and/or photographs for study; Mag. S. Sontag and A. Glaser for SEM assistance and technical support; Drs. W. Huber, A. Weissenhofer, R. Buchner, and M. Weber for support and information; and the Botanical Garden of the University of Vienna (HBV) and the Horticultural Division of the Royal Botanic Garden Edinburgh (RBGE) for caring for plant material. Special thanks go to two anonymous reviewers who contributed to substantial improvement of the paper. 
2 Author for correspondence (e-mail: anton.weber{at}univie.ac.at
)
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