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Anatomy and Morphology |
Department of Ecology, Evolution, and Marine Biology, University of California, Santa Barbara, California 93106-1467 USA; and Department of Plant Biology, Louisiana State University, Baton Rouge, Louisiana 70803 USA
Received for publication June 29, 2001. Accepted for publication December 13, 2001.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: Afzelia • Berlinia • Caesalpinioideae • Detarieae • Fabaceae • floral development • flower • Gilbertiodendron • Leguminosae • Macrolobium • Neochevalierodendron • Paramacrolobium • Tetraberlinia • zygomorphy
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Breteler and Wieringa, 1999
; Wieringa, 1999
; Mackinder, 2000
), molecular systematics (Bruneau et al., 2000
, 2001
), comparative study of wood (Gasson, Trafford, and Matthews, 2000
), vegetative anatomy (Herendeen, 2000
), pollen (Banks and Klitgaard, 2000
; Banks, Klitgaard, and Crane, 2001
), reproductive biology (Lewis, Simpson, and Neff, 2000
), and comparative floral development (Tucker, 2000a
, b
, c
, d
, 2001a
, b
, 2002
). Comparative floral ontogeny provides a basis for understanding the mechanisms that bring about the floral distinctions among related taxa. These may be heterochronic, differences in timing of shared events in development, or they may be qualitative differences, events that occur in one taxon but not in another. Both types of differences have been found in floral ontogeny of various taxa of Detarieae. One goal of this paper and other related papers is to determine which developmental character states are shared among the majority of Detarieae and which character states distinguish Detarieae from other groups of legumes. Since this group is characterized by flowers having fewer than the full complement of floral organs (21 organs) typical of most legumes, another goal is to determine whether the missing floral organs in this group result from loss (noninitiation) or suppression after organ initiation. This kind of information can only be obtained from complete ontogenetic series for each species, preferably from scanning electron microscopy (SEM). Finally, a third aim is to correlate our conclusions with those resulting from other lines of evidence.
The invaluable compendium (Polhill and Raven, 1981
) resulting from the first Legume Congress at Kew utilized and amended the classification by Léonard (1952
, 1957
) for tribe Detarieae, a notoriously confusing assemblage of caesalpinioid legumes. My comparative floral ontogenetic studies of Detarieae have shown strong correlations for some parts of Léonard's groups (i.e., Brachystegia group; Tucker, 2000a
), but not any significant intergroup distinctions. Bruneau et al. (2000)
, using molecular evidence, did not find support for Léonard's groups. The developmentally based criteria that I have used for the detarioid "Omega"-type assemblage (Tucker, 2001a
, b
) considered here include having a radially elongate and tangentially narrow postbracteole apex, rapid enlargement of bracteoles directly after their initiation so that they appear relatively large, 21 floral organs initiated, and nonhelical sepal initiation. In the first paper of this series (Tucker, 2002
) detarioid taxa with relatively moderate organ suppression were included. This second paper includes species having significant organ suppression, especially of petals and stamens. The Léonard groups represented here are the Berlinia group (Tetraberlinia), Hymenostegia group (Afzelia and Neochevalierodendron), and Macrolobium group (Gilbertiodendron, Macrolobium, and Paramacrolobium).
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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; Cowan and Polhill, 1981a
, p. 128; and label data by F. J. Breteler).
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Stamen initiation is unidirectional in the outer whorl, beginning abaxially (Fig. 13); the members of the second stamen whorl appear to initiate simultaneously (Figs. 15 and 16). The abaxial and two lateral outer stamen primordia appear slightly larger than the two adaxial in their whorl, but this difference does not persist. Similarly, the abaxial members of the inner stamen whorl exceed the others in size at early stages (Fig. 19). No overlap in time of initiation between whorls was noted.
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The stamens of the outer, antesepalous whorl enlarge and differentiate before those of the inner, antepetalous whorl. All are canted inward toward the carpels (Figs. 17–19). In the outer whorl, three primordia enlarge first: the median abaxial and the two laterals (Figs. 18 and 19); these three are persistently larger than the other two outer stamens and larger than the innerwhorl stamens during development, but all become equalized in size at maturity. The outer stamens enlarge distally as anther formation begins (Fig. 21). The microsporangia develop, delimited by a median adaxial groove (Figs. 22 and 23) and the lateral grooves (Fig. 23). The inner, antepetalous stamen primordia follow the same process of differentiation, beginning with distal enlargement (Fig. 22). In midsized buds, the outer five stamens still exceed the inner five in size (Figs. 25 and 26) but toward anthesis (Fig. 1d–e), all ten are alike. The anthers are inverted in large buds.
As the carpel heightens, its margins extend and then become appressed (Fig. 20) and finally fused (Figs. 21 and 23). Trichomes form adaxially near the base (Fig. 21) and then become more abundant around the base (Figs. 23 and 25). The gynoecium becomes short-stipitate and attached to the adaxial side of the hypanthium (Fig. 2c–e). The style is elongate and coiled in large buds (Fig. 2d–e), and the stigma is capitate.
Phyllocarpus septentrionalis Donn Smith
Phyllocarpus (Barnebydendron Kirkbride) includes two species of tall trees in tropical America in the Detarium group of Léonard. Flowers are purple or red in short racemes or fascicles at the nodes of leafless 1-yr.-old branches. The bracts and small free bracteoles are caducous. The flowers are zygomorphic with a short calyx tube, four imbricate subequal sepal lobes, and three imbricate obovate petals. The ten diadelphous stamens have a connate sheath split on the upper side; the anthers are uniform, versatile, and ovate. The ovary is stipitate and free, the style filiform, the stigma clavate, and no hypanthium is present (Baillon, 1872
; Hutchinson, 1964
; Cowan and Polhill, 1981a
, p. 133).
Floral development of Phyllocarpus septentrionalis resembles that of the previous species including acropetal, helical order of flower initiation in the racemose inflorescence, the "Omega-type" narrow postbracteole floral apex, massive bracteoles, helical initiation of five sepals, nearly simultaneous initiation of five petals, and unidirectional initiation of the five antesepalous stamens.
One large petal, nine or ten stamens (Berlinia and Tetraberlinia)
The genus Tetraberlinia (Cowan and Polhill, 1981b
, p. 138) includes four species of tropical African forest trees in Guinea and Congo. Wieringa (1999)
showed that Tetraberlinia is close to Aphanocalyx and Monopetalanthus, previously studied (Tucker, 2000a
).
Tetraberlinia tubmanniana J. Léonard (Figs. 28–56)
Tetraberlinia tubmanniana is a large forest tree bearing compound racemes (Wieringa, 1999
) that contain 4–14 flowers on each of several side branches. The bracteoles are ovate, asymmetric, and velvety pubescent (Wieringa, 1999
). The zygomorphic flowers (Fig. 28a and e) have five white to pale greenish sepals, densely pubescent outside, with the adaxial two nearly completely fused. The five petals include a large adaxial yellow petal, 6–8.5 mm long with a short wide claw; the limb is rectangular and ciliate margined. The lateral petals are white and linear to 4.5 mm long. There are ten uniform stamens with filaments 12–15 mm long, of which nine are basally connate. The ovary is stipitate with an elongate style and a heart-shaped stigma; the stipe is inserted at the base of the cupular hypanthium (Fig. 28d; Wieringa, 1999
). Tetraberlinia is included in Berlinia by Hutchinson (1964)
and is in the Berlinia group (Cowan and Polhill, 1981b
, p. 138). It is placed in the Macrolobium group of Breteler and Wieringa (1999
; Wieringa, 1999
). Wieringa's phylogenetic analysis (1999)
shows Tetraberlinia as the monophyletic sister group to Bikinia/Aphanocalyx.
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for explanation), with small projections adaxially and abaxially. The bracteoles enlarge massively at this time (Fig. 32) and remain in contact with the floral apex around its entire periphery.
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The order of petal initiation was not determined, because the abaxial petal sites were obscured in the only floral bud found at this stage (Figs. 36 and 37). The adaxial and one lateral adaxial petal primordium have initiated, but it cannot be determined whether the abaxial ones have initiated. After all five petal primordia have initiated (Figs. 38 and 39), they are equal in size, although the adaxial one is broad and flat while the other four have increased more in height.
The timing of carpel initiation was not determined precisely; it is initiated concurrently with either the petals or the outer stamens (Figs. 36 and 37). The carpel primordium is relatively small at initiation in this species, approximately the same size as individual stamen or petal primordia at the same time. In related detarioid genera, the carpel is usually about twice the basal diameter of any other floral organ just after initiation. The carpel in this species enlarges at first as a hemispherical dome (Figs. 38 and 39).
The outer, antesepalous stamens are initiated bidirectionally, starting with two laterals (Figs. 38 and 39). After the single abaxial and two adaxial members have initiated in the same whorl, they appear equal in size (Fig. 42). The stamen primordia of the inner antepetalous whorl begin initiation on the abaxial side (Fig. 39), so are unidirectional, although they all appear equal in size very early (Fig. 42). Initiation overlaps in time between the two whorls. The innerwhorl stamen primordia are rapidly covered by the enlarging outer floral organs, but some can be seen in Figs. 50, 53, and 54. No ring meristem is present, although it does occur in taxa thought by Wieringa (1999)
to be closely related to Tetraberlinia. The ring meristem will be considered more at length in the Discussion.
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The petal primordia remain short and undeveloped until after all other organs are present. Laminar growth becomes evident as the petals grow in height (Figs. 47 and 48). Four of the petals remain short (Figs. 51–53, at arrowheads), while the fifth enlarges (Figs. 28e and 51–55). At anthesis only one petal is evident (Fig. 28a).
The outer, antesepalous stamen primordia are larger than the innerwhorl stamen primordia at any one stage and also begin differentiation first. Anthers and filaments begin differentiation in the outer stamens (Figs. 49 and 50); later stages with elongate filaments and mature anthers are seen in Figs. 53–56. The innerwhorl stamens begin differentiation (Fig. 50), follow the same ontogeny as the outer stamens, and appear fully differentiated in Fig. 54. The anthers of all stamens change from erect (Figs. 52 and 53) to inverted positions (Fig. 54) in bud, and then become versatile at anthesis (Fig. 28a). All ten stamens are functional and alike in the flower at anthesis.
The carpel is a high-convex mound at a height of about 80 µm (Fig. 43). The adaxial side flattens (Fig. 44) and then the cleft becomes visible at an approximate height of 120 µm (Fig. 45). The margins become appressed and remain so during subsequent development. At a height of about 270 µm the tip becomes attenuate as the style starts to form (Fig. 50). In the large bud, the style is linear, glabrous, coiled, and folded over the summit (Figs. 28a and 53). Trichomes begin to form over the ovary at a height of about 270 µm (Figs. 49 and 50), and close to anthesis the trichomes completely obscure the outline of the ovary (Fig. 53). Tetraberlinia tubmanniana conforms to the type of organ reduction in Fig. 1b, with four petals reduced in size but no reduction among the ten functional stamens.
Berlinia grandiflora (Vahl.) Hutch. & Dalziel
This species is similar to Tetraberlinia in its floral ontogeny so is not illustrated. The genus Berlinia sensu lato Hutchinson includes 15 tree species from tropical Africa (Cowan and Polhill, 1981b
) and is in the Berlinia group. The genus is being monographed by Mackinder (2000)
, who divides it into two groups based in part on petal number (one vs. five).
Berlinia grandiflora is a small tree 4–10 m high. It has racemose, helically arranged inflorescences with coriaceous, caducous bracts; the bracteoles are large, green, glaucous outside, enclosing the floral buds, then spreading and persistent in flower. The large showy zygomorphic flowers have five sepals that are thin, imbricate, pale green outside, and cream-white inside. The five petals include a large standard petal (6–7 cm long), white with a yellow spot at center, clawed with a broadly circular limb, and two to four small linear white petals. Nine stamens are attached to a short filament tube at base that is open adaxially, and the adaxial median stamen is free. The stamens have elongate white filaments and uniform oblong dorsifixed anthers. The stipitate ovary is adnate to the elongate hypanthium (Thompson, 1924
; Hutchinson, 1964
; Cowan and Polhill, 1981b
). Berlinia grandiflora is interesting in having synchronous early floral bud development in its racemose, few-flowered inflorescences. Order of organ initiation is helical among sepals, unidirectional among stamens, with each whorl starting on the abaxial side. An exception in one flower had the first stamen primordia lateral in the outer whorl, quickly followed by the abaxial median stamen that is usually the first in that whorl. Late stages of floral development were not available.
One large petal; seven large stamens (Afzelia) (Figs. 57–88)
Afzelia quanzensis Welw. is in the Hymenostegia group (Cowan and Polhill, 1981a
) and includes 13 to about 30 species of trees of tropical southeast Asia, tropical Africa, South Africa, and Madagascar. The flowers are in few-flowered terminal panicles or racemes (Léonard, 1952
). The tomentose, ciliate-margined bracteoles are ovate, concave, valvate, and subpersistent. They enclose the floral buds to a length of about 4 mm. They separate as the bud enlarges, and the sepals become protective. The flowers (Fig. 57a) are large (about 5–6 cm high), zygomorphic, with four elliptic or obovate imbricate sepals, the outer two of which are largest and are the only ones visible externally in bud. There is one large petal (Fig. 57a and d), clawed, bilobate, and unguiculate, red, 2–4 cm long and 2–3 cm wide, while the other petals are rudimentary or absent. There are seven functional stamens (Fig. 57a, c, and d) in A. quanzensis, with elongate declinate filaments and ovoid anthers, plus two staminodes in our material (Fig. 57c). Léonard (1952)
reported seven free fertile stamens in A. quanzensis plus two filiform staminodes, so there is some variation as to the number and degree of stamen suppression. The filaments are long exserted, and the anthers are small, oblong, and dorsifixed with longitudinal dehiscence (Fig. 57a). The gynoecium has a stipitate pubescent ovary, elongate style, and a small truncate subcapitate stigma; the gynoecial stipe is laterally adnate to the elongate hypanthium (Fig. 57b; Thompson, 1924
; Léonard, 1952
; Hutchinson, 1964
; Cowan and Polhill, 1981a
).
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Afzelia quanzensis, organ development
The sepals become relatively thick, with the abaxial and two adaxial ones elongating more than the lateral two (Fig. 66). These lateral sepals (Fig. 70) remain the smallest through midstage. The two adaxial sepals become laterally confluent so that the calyx appears tetramerous (Fig. 57a and d).
The five petal primordia are initially equal in size and shape (Fig. 71), but at midstage the median adaxial petal (vexillary petal) grows marginally (Figs. 74 and 79), more so than the other four. In Fig. 80 the vexillary petal, 0.5 mm in height, is incurved marginally; the much narrower and shorter lateral petals (Fig. 79) are not touching. With further enlargement, a claw and a large enveloping limb become visible (Figs. 81, 83, 84, and 86) in the vexillary petal. The other four petals do not enlarge further but persist as rudiments (Figs. 86 and 87 at arrowheads).
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The carpel develops a cleft at a height of about 220 µm (Figs. 71 and 72). The margins remain appressed during subsequent enlargement (Figs. 75 and 76). With enlargement, a laterally compressed glabrous ovary and an elongate coiled style develop (Figs. 57a, 82, 85, and 88). Differential growth in late stage reorients the gynoecium to the adaxial side of the short hypanthium (Fig. 57b). The flower of Afzelia quanzensis corresponds to the type of organ reduction in Fig. 1c, with the corolla reduced to one petal and the androecium somewhat reduced, with seven functional stamens.
One large petal; three large stamens (Gilbertiodendron, Macrolobium, and Paramacrolobium)
Gilbertiodendron (Figs. 89–122)
Two species were studied; the early stages are similar, so are shown for only one species. Some older stages are present in one but not available in the other. The genus includes 26 tree species of tropical Africa and is in the Macrolobium group. Inflorescences in the genus are paniculate to racemose, axillary, terminal, or on old wood. Small helically arranged bracts subtend individual flowers.
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, and label data by Wieringa; see Table 1).
Gilbertiodendron klainei, organogenesis
The sequence and stages are similar in the two species with minor differences, so only G. klainei is described and illustrated. The apical meristem of the inflorescence initiates bract primordia in helical acropetal succession (Fig. 90). A floral apex, wide tangentially and narrow radially, initiates in each bract axil. Paired bracteoles are initiated by the floral apex in rapid succession (Fig. 91) and grow rapidly to surround the floral apex before and during floral organogenesis (Fig. 98). The postbracteole floral apex is narrow and tapered adaxially and abaxially, although the abaxial side of the apex is usually truncate (Fig. 92).
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Petal initiation is unidirectional, with the first four appearing simultaneously (Figs. 94–96) and the adaxial petal lagging in time of initiation. The five petal primordia remain small and uniform in size through midstage (Figs. 100 and 101). The carpel is initiated concurrently with petal initiation (Figs. 94 and 95).
The order of initiation in each of the two whorls of stamens is presumed to be unidirectional. The first outerwhorl stamen primordium, median on the abaxial side, was obscured by a sepal in all preparations, but is assumed to have initiated first on the basis of its relative size in Fig. 102. The laterals are initiated next (Figs. 98 and 99 at arrowhead for one lateral primordium and Fig. 100 for both laterals). The two adaxials are formed last (Fig. 102). The order among the inner antepetalous stamen primordia is presumed to be unidirectional from the abaxial side, based on the abaxial sites being slightly larger than the others in early stages (Figs. 100 and 101). The inner stamen primordia rapidly become equalized in size shortly after their initiation (Figs. 102 and 103). No overlap was observed in time of initiation between whorls.
Gilbertiodendron klainei, organ development
The bracteoles become massive and surround the developing floral bud during early organogenesis (Fig. 98). They ensheathe the floral bud throughout development (Fig. 89b and d). The sepals form a calyx cup with five lobes (Fig. 101); the two adaxial sepals do not become confluent, as in many other Detarieae. The sepals become linear-lanceolate (Fig. 119) in large bud. At anthesis, the sepals are linear, acutely tipped, relatively thin and membranous, and are flared outward (Fig. 89a).
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Of the ten stamens initiated, only three become large and functional. These three are the lateral and abaxial median members of the outer, antesepalous whorl, which begin to enlarge precociously during midstage (Figs. 102 and 104). The strong variation in size among stamen primordia of the outer whorl is visible in Figs. 105 and 107. In Fig. 112, most organs are removed, showing the stamen rudiments; two (A) are in the outer antesepalous whorl and one (a) is in the inner antepetalous whorl. Stamen differentiation proceeds first in the members of the outer whorl and then in the inner whorl. Each stamen primordium enlarges distally to form the anther (Fig. 109), followed by formation of the microsporangia, delimited by a median adaxial groove and lateral grooves (Figs. 110 and 113). The anthers are basifixed early in their differentiation (Figs. 109 and 110), but become dorsifixed in late stage (Figs. 115 and 121) by differential growth. In bud (Fig. 122), only the three large stamens can be seen. The filaments elongate rapidly at anthesis so that the three large stamens become exserted. The six others remain small or reduced (Fig. 89e). All of the stamens, functional and reduced, are attached on a short, fleshy tube; earlier reports held that only the innerwhorl stamens were on a tube (Cowan and Polhill, 1981b
; Bruneau et al., 2000
).
The carpel primordium develops a cleft (Fig. 103) at the same time that the last whorl of stamens is initiated. With height increase, the carpellary margins expand in area. The margins are gaping and unfused during the start of ovule initiation at a carpel height of about 340–520 µm in G. klainei (Figs. 105–108), but they are appressed and then fused at this stage in G. brachystegioides (not shown). The margins become appressed and sealed by a height of about 640 µm (Fig. 111). The carpel becomes tapered and a style develops (Fig. 116) by a height of about 800 µm. The style is coiled in bud (Fig. 89c). Sparse trichomes develop on the adaxial and lateral sides of the carpel (Figs. 89a and 122). The gynoecium base is in a depressed pit in late stages (Fig. 112). The flowers of Gilbertiodendron species exemplify the high degree of organ reduction diagrammed in Fig. 1d, with four of the five petals and seven of the ten stamens reduced.
Paramacrolobium coeruleum
This tropical tree genus is monotypic and is native to tropical West Africa. Its floral development is essentially similar to that of Gilbertiodendron brachystegioides so is not illustrated. The inflorescences are compact distichous corymbs with acute, glabrous floral bracts subtending flowers in two vertical rows. Order of flower enlargement in an inflorescence is unusual in that the uppermost lateral floral bud enlarges before those lower down in the inflorescence. The paired bracteoles are thick, fleshy, glabrous, elongate, valvate, fused, and persistent; they enclose the floral buds from the time the latter are extremely minute through the time of anthesis. The flowers have two persistent bracteoles, zygomorphic symmetry, four (rarely five) sepals (the adaxial one bifid and wider than the rest), and a short calyx tube. They have five petals, including one large petal and four rudiments, three functional stamens, 4–5 staminodia, and a stipitate gynoecium with capitate stigma. Hutchinson (1964)
says the nine stamens are fused basally, with 3–5 fertile and exserted, 4–6 small and staminodial. The gynoecium is attached to one side of the hypanthial tube.
Developmentally, Paramacrolobium coeruleum has a postbracteole floral apex that is elongate sagittally and narrow tangentially, although it is more circular than in most other "Omega"-type taxa. The bracteoles enlarge and enclose the floral bud early and completely. Organ initiation is helical among sepals (with the first abaxial and nonmedian), unidirectional among petals and antesepalous outer stamens, all starting on the abaxial side first. The carpel initiates concurrently with the petals. No initiation stages were observed of the antepetalous stamens. Three antesepalous stamens (the abaxial and two laterals) exceed the rest in size by midstage and maintain this advantage throughout development. They become the functional stamens; the rest become staminodia.
Macrolobium acaciifolium Benth. and M. crassifolium (Baillon) Léonard
Macrolobium includes 130+ species of trees, lianas, and large shrubs from tropical America and Africa. The inflorescence of M. crassifolium has bracts and subtended flowers helically arranged. The valvate, sepaloid, persistent bracteoles enclose the buds. Flowers are small, zygomorphic, and have four imbricate sepals (the adaxial two confluent). One petal is larger than the rest and orbicular, while the other petals are rudimentary. Three large fertile stamens have filiform filaments, dorsifixed versatile anthers, and longitudinal dehiscence; the other stamens are reduced as staminodia or are absent. The stigma is terminal, the style is filiform, and the ovary is short stipitate and laterally attached (Thompson, 1924
; Léonard, 1952
; Hutchinson, 1964
; personal observations). The genus is in the Macrolobium group (Cowan and Polhill, 1981b
) and is characterized by having racemose inflorescences, one large petal and 1–4 minute rudiments, three large stamens plus reduced staminodes, all stamens free and in one whorl, and an exserted stipitate gynoecium (Thompson, 1924
; Cowan and Polhill, 1981b
).
Organogenesis and development of Macrolobium species are very similar to those of species of Gilbertiodendron just described. The floral apex of M. crassifolium is the "Omega"-type at bracteole initiation, and the massive bracteoles enclose the floral bud early in development. Organogenesis is helical among five sepals and unidirectional in the petal and stamen whorls, all starting on the abaxial side. The carpel is initiated concurrently with the first-initiated antesepalous stamens. Three antesepalous stamen primordia (the median abaxial and the two laterals) are disproportionately large by midstage; these later become the functional stamens. The vexillary petal remains small until late in development in species of Macrolobium, as in Gilbertiodendron.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Shared character states
The taxa studied here have most of the same assemblage of early-ontogeny character states that were reported in the Brachystegia group of Detarieae (the "A" or "Omega"-type in Tucker, 2000a
). They have the "Omega"-type floral apex after bracteole initiation, precociously enlarged bracteoles just after initiation that encircle 90% of the circumference of the postbracteole floral apex, which tends to be tapered adaxially and abaxially. The character states that they share with the "circular apex" or "B" type group (Amherstia, Cynometra, Schotia, Tamarindus, Crudia, etc.; Tucker, 2000d
, 2001a
, b
) include helical initiation of sepals in most, complete calyx and corolla initiated, and no ring meristem (see following paragraph), which are probably plesiomorphic character traits. Zygomorphy and a reduced number of organs are the character traits distinguishing the present taxa from those Detarieae covered in a previous paper (Tucker, 2002
). The flowers of the present taxa are strongly zygomorphic at anthesis. This zygomorphy is primarily expressed as one petal much larger than the others and by suppression of several of the stamens: three stamens suppressed in Afzelia or seven stamens suppressed in Gilbertiodendron, Macrolobium, and Paramacrolobium.
Ring meristem
In a few detarioid taxa, the floral meristem forms a continuous raised ring around the center of the apex; organ primordia are initiated upon this ring. No ring meristems occur in any of the species included here. Tetraberlinia tubmanniana might have been expected to have one in view of its relationship as sister group to the Aphanocalyx/Bikinia clade in the phylogenetic analysis by Wieringa (1999)
. A ring meristem has been found in Monopetalanthus durandii (Bikinia durandii), Aphanocalyx djumaensis (both in the group studied by Wieringa) and two species of Brachystegia (Tucker, 2000a
), and Microberlinia bisulcata (Tucker, 2002
). The ring meristem innovation was suggested as a possible defining character for the Brachystegia group (Tucker, 2000a
) that includes these taxa except for M. bisulcata.
Effect on organogeny of suppressed vs. lost organs
Many of the taxa studied here have reduced numbers of floral organs (petals and stamens as diagrammed in Fig. 1a–d) at anthesis. However, in all, the full complement of organs is initiated in each whorl, and the reduced organ number is due to suppression after initiation. The "missing" organs can be seen to initiate, and rudiments are usually detectable even at anthesis. The contrasting effect on subsequent organogeny between organs that initiate and those that fail to initiate has been emphasized by Tucker (1988a
, b
, 2000c
).
Systematic relationships
Taxonomic relationships among genera of Detarieae continue to be unclear and confusing. The molecular- and morphology-based analyses by Bruneau et al. (2000
, 2001
) found none of the ten generic groups of Polhill (1994
, based on a smaller group proposed by Léonard, 1957
) to be monophyletic. Molecular data (Bruneau et al., 2000
, 2001
) indicate that Detarieae as a whole (including Macrolobieae) is monophyletic. The tribe Macrolobieae sensu Bruneau et al. (2000)
, after Amherstia, Humboldtia, Macrolobium, and Tamarindus are removed, is monophyletic and is derived from Detarieae s. str., but the Macrolobieae of Breteler (1995
; Breteler and Wieringa, 1999
), which includes the latter genera, is not monophyletic.
Three clades (A, B, C) were designated by Bruneau et al. (2000)
within Detarieae sensu lato. Their Clade C comprises the reconstituted tribe Macrolobieae and includes three taxa in the present paper: Berlinia, Gilbertiodendron, and Tetraberlinia, as well as most of the taxa studied in the first of the two summary papers (Tucker, 2002
). Several other genera studied here (Afzelia, Macrolobium, Neochevalierodendron, and Paramacrolobium) are in Detarieae sensu stricto (Clade B of Bruneau et al., 2000
).
Tucker (2001a
, b
) established two groups based on early floral developmental character states: an "Omega" group and the "circular" group. The "Omega" group share an assemblage of developmental character states: early and massive bracteole enlargement; a radially elongate, narrow postbracteole floral apex resembling the Greek letter Omega; first sepal and first petal initiating simultaneously but on abaxial and adaxial sides, respectively; and suppressed or delayed timing of initiation of other sepals and/or petals. The "Omega" group includes taxa in the Macrolobieae clade (Bruneau et al., 2000
), plus Clade B pro parte (Afzelia, Hymenostegia, and Neochevalierodendron), and one genus in clade A, Sindora. Most of Tucker's "circular apex group" (Amherstia, Brownea, Crudia, Cynometra, Paramacrolobium, Saraca, and Tamarindus; Tucker, 2000b
, d
, 2001a
, b
, this paper) are in Clade B of Bruneau et al. (2000)
; the exception, Schotia, is in Bruneau et al.'s Clade A. Tucker (2001a
, b
) had very few (2 out of 24) of the taxa in Clade A for floral ontogenetic study, so no speculation is possible as yet as to its correlation with either of Tucker's developmental assemblages. Two taxa, Paraberlinia and Sindora, have an unusual order of organ initiation and will be considered in a future publication (unpublished data). A phylogenetic analysis that utilizes ontogenetic data is also under way with colleagues.
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FOOTNOTES |
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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