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Structure, Development, and Morphogenesis |
Department of Biology (Ecology, Evolution, and Marine Biology), University of California, Santa Barbara, California 93110 USA; and Department of Plant Biology, Louisiana State University, Baton Rouge, Louisiana 93106 USA
Received for publication May 10, 2001. Accepted for publication October 9, 2001.
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Key Words: aestivation • Cadia • Fabaceae • floral development • flower • Leguminosae • Papilionoideae • radial symmetry • Sophoreae
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). The tribe has recently been shown to be nonmonophyletic (Herendeen, 1995
; Doyle et al., 2000
; Ireland, Pennington, and Preston, 2000
) and is currently in the process of dismemberment, with certain woody taxa of sophoroids appearing to be more closely related to some elements of tribes Swartzieae, Dalbergieae, and others (Ireland, Pennington, and Preston, 2000
; Pennington et al., 2000, 2001
). Recent molecular-based analyses (Doyle et al., 2000
; Pennington et al., 2000, 2001
) place Cadia as sister to Calpurnia (tribe Podalyrieae) but embedded within a clade containing other sophoroid taxa. Cadia, a genus of small shrubs from Arabia, Madagascar, and eastern Africa, has long been of interest because of its radial floral symmetry and atypically unstable petal aestivation (van der Maesen, 1970
; Tucker, 1984, 1987
), in contrast to the prevailingly uniform, descending cochleate aestivation of nearly all other Papilionoideae.
The tribe Sophoreae sensu Polhill (1981, 1994)
includes the putatively least specialized and most plesiomorphic taxa of the large subfamily Papilionoideae of legumes. As originally conceived by Bentham (1841)
the tribe was considered transitional between papilionoids and the subfamily Caesalpinioideae. The emphasis on the heterogeneity in Sophoreae (Polhill, 1981
) prompted examination of the pollen structure (Ferguson, Schrire, and Shepperson, 1994
), endothecial characters (Manning and Stirton, 1994
), and wood (Gasson, 1994
). Because of the recent surge in interest in taxa of Sophoreae sensu lato (s.l.), the floral ontogeny of Cadia purpurea Ait. is presented, together with updated comments on its putatively plesiomorphic character states.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Buds were preserved in liquid fixative in the field, transferred to 95% alcohol, and dissected in the laboratory. For scanning electron microscopy, dissected buds were dehydrated up to 95% ethyl alcohol so they were crisp for ease of dissection. The dissected pieces were further dehydrated through an acetone-ethyl alcohol series, critical point dried with CO2, and mounted on aluminum stubs with colloidal graphite. The pieces were coated with gold-palladium, and buds were studied and micrographs taken at 25 kV with either a Hitachi S-500 (Hitachi Co., Tokyo, Japan) or a Cambridge S-260 (Cambridge Scientific Instrument Co., Cambridge, UK) scanning electron microscope in the Department of Botany, Louisiana State University, Baton Rouge, Louisiana, USA.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). The flowers are white, cream, rose, or purple and are solitary in leaf axils or in few-flowered racemes. Those of Cadia purpurea are rose-colored and solitary. Each flower (Fig. 1a–d) has a campanulate calyx cup with five short lobes; five free, obovate petals with a very short claw; ten free, subequal stamens with versatile dorsifixed anthers; and a solitary short-stipitate carpel with a small terminal stigma (Hutchinson, 1964
; personal observations). Petal aestivation (Fig. 2) is highly variable and strongly atypical of papilionoid flowers, appearing completely random rather than descending cochleate as in the great majority of the subfamily. The highly variable petal aestivation was studied by van der Maesen (1970)
who reported on Ross's unpublished work and by Tucker (1984)
. Ross found 21 different types of aestivation, including ascending cochleate (typical of higher Caesalpinioideae), descending cochleate (as in most Papilionoideae), quincuncial (as in Apocynaceae), and numerous other variations of these types. Tucker (1984)
reported eight types of petal aestivation in a smaller sample of C. purpurea; this work will be discussed later.
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The carpel is initiated (Figs. 10 and 11) from the central part of the floral apex directly after petal initiation. It remains highly convex, much exceeding the other floral organs in height (about 80 µm in Fig. 13) during early stages. The carpel primordium first becomes flat on its adaxial side (Fig. 15) and then develops an adaxial dimple at a height of about 100 µm (Fig. 16). The adaxial depression deepens as a carpel cleft (Figs. 17 and 18).
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The inner-whorl stamen primordia initiate centripetal to the petal bases (Figs. 13–16). The stamen primordia differ in size early, before other differentiative changes; the outer antesepalous stamens enlarge before the others (Fig. 17). Atypical conditions seen include a tetramerous flower and one in which the vexillary stamen was missing.
Organ enlargement and differentiation
The sepal primordia enlarge uniformly, with five lobes atop a calyx tube that is relatively thick and confluent by early petal stage (Fig. 1a, c, and Fig. 9). In bud, the sepal lobes remain separate but valvate and grow as fast as the calyx tube below, so that the lobes persistently represent about 40% of the total bud height at each stage. The free sepal lobes are approximately equal in size and shape at maturity (Fig. 1a). Densely packed trichomes on the calyx cup cover the bud surface just before anthesis (Figs. 25 and 26).
When all petal and stamen primordia have been initiated (Figs. 17 and 18) the petals are the same height as the stamen primordia. The petal primordia remain small (about 75 µm in Figs. 19 and 20) while the other primordia start to enlarge. When the inner stamens start their differentiation, the petals are about 140 µm high (Fig. 22). The petal margins enlarge and approach each other at a height of about 1 mm (Figs. 28–30) at the time when microsporangia have differentiated in all stamens and while the floral receptacle is expanding in diameter. Overlap of petals begins at a petal height of about 2 mm, when the antesepalous stamens are about 3.5 mm high. The petals and stamens are attached on the rim of the shallow hypanthium (Figs. 1b, 26, and 29) close to anthesis. Petal aestivation in Cadia (Fig. 2a–i; Tucker, 1984
) varies greatly and will be examined in the Discussion.
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The inner (antepetalous) stamen primordia begin to differentiate at about 140–170 µm in height (Fig. 23) when each first shows a terminal notch. Some flowers differ slightly in antepetalous stamen height along the sagittal plane. The receptacle grows differentially below the stamen bases to bring the inner stamens into the same ring as the outer ones (Fig. 21) and eventually into positions in which the inner ones overlap outside the outer ones (Fig. 22). Curiously, the antepetalous (inner) stamens expand outside the whorl of antesepalous stamens (Fig. 22, 27, and 28) at this stage due to differential growth of the receptacle below the stamen bases. Microsporangia become evident at a height of 290–350 µm (Fig. 22). By a stamen height of about 1.2 mm, the anthers are dorsifixed (Figs. 25 and 26). At anthesis, all ten stamens appear to be part of one whorl (Fig. 30) and filaments are broad basally and taper upward (Fig. 1b). The filaments have swollen knob-like pads internally where they are attached to the rim of the hypanthium (Fig. 1c).
The carpel primordium is about 100 µm high when the cleft is first visible (Fig. 16) and about 130 µm when the cleft becomes well defined (Fig. 18). As the carpel primordium heightens, the cleft becomes adaxial (Fig. 17); the petal and stamen primordia are undifferentiated at that stage. Some carpel clefts are obliquely aligned (not shown). At 400 µm in height the carpel has a flared base and the cleft is restricted to the distal half (Fig. 23). Most elongation occurs in the portion of the carpel including the cleft (Fig. 24), which is also the level of ovules. Carpel margins are completely fused at this carpel height (about 800 µm) except for a small opening near the base (Figs. 24 and 26). The carpel remains cylindrical and straight (Figs. 1b, c, and 26) with a slightly tapered tip. The stigma is truncate and covered by papillate hairs (Fig. 31).
The receptacle expands radially to form a disk around the base of the carpel by the time that the latter is about 730 µm high (Fig. 24). A shallow hypanthium begins to form by a carpel height of about 1.45 mm (Fig. 26) as the result of zonate growth in height below the bases of the petals and stamens. At anthesis, the hypanthium remains shallow; the carpellary stipe is attached centrally (Figs. 1c and 34).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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). Recently, morphological and molecular evidence has shown Sophoreae to be nonmonophyletic (Herendeen, 1995
; Doyle et al., 2000
, Ireland, Pennington, and Preston, 2000
) and its taxa to be inextricably intermixed with taxa of tribe Swartzieae. Sophoreae is currently in the process of dismemberment, with certain woody taxa of sophoroids appearing most closely related to some elements of tribes Swartzieae, Dalbergieae, and others (Ireland, Pennington, and Preston, 2000
; Pennington et al., 2000, 2001
). Polhill (1994)
assigned Cadia to tribe Podalyrieae; a recent molecular-based analysis (Doyle et al., 2000
) placed Cadia as sister to Calpurnia in Podalyrieae, both embedded within a clade otherwise consisting of taxa of Sophoreae. Cadia, a genus of small shrubs from Arabia, Madagascar, and eastern Africa, has long been of interest because of its radial floral symmetry and unstable petal aestivation (van der Maesen, 1970
; Tucker, 1984, 1987
), in contrast to the prevailingly uniform, descending cochleate aestivation of nearly all other papilionoids.
Cadia purpurea shares many aspects of floral development with other papilionoids that have been investigated. In a sample of 32 genera examined (unpublished data) representing 15 tribes of papilionoids, the floral organ whorls are initiated in acropetal order except for the carpel. The order of organ inception in each whorl is unidirectional from the abaxial side in the great majority of these taxa, as it is in C. purpurea. Sepals are initiated unidirectionally in 31 species and in modified helical order in Dalbergia (Klitgaard, 1999
). Petals initiate unidirectionally in 30 species having five petals (Ateleia is an exception, as it has only one petal) and initiate simultaneously in Calpurnia. Stamens initiate unidirectionally in 30 out of 32 genera, bidirectionally in the inner whorl in Pterocarpus (Klitgaard, 1999
), and in erratic order in stamen whorls of Ateleia (Tucker, 1990
). This relatively uniform order of organogeny contrasts with that among the other subfamilies: helical or whorled in Mimosoideae and in diverse order (helical, simultaneous, or unidirectional) among Caesalpinioideae (Tucker, 1985, 1987
).
The flower of Cadia purpurea differs from most other papilionoids by remaining radially symmetrical at midstage through late stages of development. Also, the petal primordia remain small with little marginal growth until later than in most other papilionoids. Cadia purpurea has an essentially plesiomorphic flower with few character states that could be considered specializations. Among these are the calyx cup (because sepals are initiated individually and only become connate later in development), dorsifixed anthers (because anthers are basifixed early in ontogeny among papilionoid legumes), and a gynoecial stipe (since the ovary is sessile early in ontogeny). The hypanthium (a shallow one) and the enlarged, knob-like filament bases are also specializations that are expressed late in ontogeny. Specialized character traits generally are expressed late in floral ontogeny (Tucker, 1997
).
Radially symmetrical flowers among papilionoids such as Cadia have been assumed to be basal (Polhill, 1981
). However, Pennington et al. (2000)
interpret their recent molecular-based phylogenetic analysis as showing nine apparent reversals from the prevailingly zygomorphic state among Papilionoideae. The 23 genera of nonpapilionoid types listed by Pennington et al. (2000)
can be classified into two groups: one group with zygomorphic flowers but atypical among papilionoids in having only one petal or more than ten stamens (e.g., Amburana, Ateleia, Bobgunnia, Bocoa, Cyathostegia, Exostyles, and Swartzia) and one group with radially symmetrical flowers (e.g., Acosmium, Amphimas, Cadia, Cyathostegia, Dicraeopetalum, Harleyodendron, Holocalyx, Lecointea, Lovanafia, Myrocarpus, and Zollernia). The Cadia/Calpurnia clade is sister to Sophora, a genus with papilionoid flowers (Tucker, 1994
). However, in several Sophora species and other zygomorphic papilionoids (Tucker, 1984, 1985, 1987, 1989, 1993, 1994
; Tucker and Stirton, 1991
) flowers appear radially symmetrical at midstage. Zygomorphy is expressed late in ontogeny in all of these taxa. In contrast, flowers such as Cadia purpurea retain radial symmetry from midstage on through the time of anthesis. One can then visualize the papilionoid phylogenetic tree as consisting of taxa that all are radially symmetrical up through midstages of development. In the taxa that appear zygomorphic at anthesis, those changes are brought about late in development. Those taxa that appear radial at anthesis are neotenic in that they lack the final events in development that would express zygomorphy. The nine taxa that Pennington et al. (2000)
asserts have undergone reversals could alternatively be considered taxa that are neotenous (retaining the juvenile state of radial symmetry).
Unstable petal aestivation
The remarkable variation in pattern of petal aestivation in Cadia purpurea, with 21 patterns reported (van der Maesen, 1970
), contrasts strongly with the highly canalized pattern in other Papilionoideae of descending cochleate arrangement. Petal aestivation in Cadia purpurea is highly variable, in contrast to most other papilionoid flowers (Fig. 2j). Variations reported by Ross (van der Maesen, 1970
) and by Tucker (1984)
included the standard petal inside the wings, standard half inside and half outside, wings both outside keel, wings both inside keel, wings half inside and half outside, and a quincuncial imbricate pattern (Fig. 2a–j). Yet a developmental explanation for the variable aestivation in Cadia purpurea is more elusive than was expected (Tucker, 1984
). Several hypotheses were envisioned that might explain the arrangement, which contrasts with petal arrangement in other papilionoids. Those ideas, tested in sectioned and whole flowers and ruled out by Tucker (1984)
, include atypical order of petal initiation (negative); atypical overlap of the petal bases (they never overlap at that level); oblique insertion of the petal bases (negative); influence of the sepal positions or sizes (negative); and relatively more cell division on the abaxial or adaxial side of the margins of certain petals (negative).
The answer appears to be the converse of the last proposed possibility, together with prolonged delay in petal enlargement. Sections of C. purpurea petals were compared with those of Sophora japonica (having descending cochleate aestivation as in most papilionoids) at the stage where petals are about to make contact. In Sophora, the petal margins that will be outside the others grow essentially straight, while the petal margins that will finally be enclosed arch inward as they enlarge more on the abaxial side than on the adaxial side. Cell division rates on the abaxial and adaxial sides of the petals concerned did not appear to differ. In Cadia, in contrast, the petal margins all have a similar marginal growth pattern, with none showing marked inward curvature. When adjacent petal margins meet in Cadia, chance appears to determine which margin will grow outside the other.
Delayed petal enlargement (about 2 mm high at the beginning of petal overlap) also may help to produce the unusual patterns of aestivation in Cadia. Among other Sophoreae, petal overlap is first seen at petal heights of about 0.44 mm in Sophora japonica, 0.5 mm in S. affinis, 0.72 mm in S. davidii, and 0.9 mm in Castanospermum australe (unpublished data). Another papilionoid group with prolonged delay before petal overlap is the Lecointea group of Swartzieae s.l.; petals overlap at about 1 mm height in Zollernia splendens, 1.3 mm in Harleyodendron unifoliolatum, about 2 mm height in Lecointea hatschbachii, and 2.7 mm in Exostyles venusta (V. de F. Mansano and S. C. Tucker, unpublished data). In a few examples from other papilionoid tribes, petals first overlap at about 0.38 mm in Psoralea pinnata (Psoraleeae) and at about 0.78 mm in Pisum sativum (Vicieae). Petal overlap begins before petals reach 1 mm height in other papilionoids examined, but in Cadia and the Lecointea group, petals remain small while the floral receptacle expands greatly in diameter, enlarging distances between adjacent petal bases. While the petal bases do not themselves overlap, the significantly larger size of the Cadia petals and larger interpetal spacing at the time of overlap may be important factors that prevent a uniform process of aestivation.
Aestivation in Cadia lacks the strong developmental controls found in other papilionoid corollas. The type of uniform marginal growth that persists in Cadia is characteristic of young petal primordia in all papilionoids, before the petals are large enough to come into lateral contact. The type of aestivation in Cadia results from chance, since each petal margin has a 50 : 50 chance of becoming an "outer" or an "inner" petal. The petal aestivation of enlarging petals in Cadia may be considered an example of neoteny or paedomorphosis, since the juvenile condition of equilateral marginal growth prevails throughout petal development.
Castanospermum (Sophoreae; Polhill, 1981
) and Exostyles (Swartzieae; Pennington et al., 2000
; V. de F. Mansano and S. C. Tucker, personal observations) also have atypical, variable petal aestivation for papilionoids. V. de F. Mansano (Universidade Estadual de Campinas, Campinas, Brazil; personal communication) reports unstable petal aestivation in some other taxa of the Lecointea group of Swartzieae s.l.
Sophoreae: which groups are monophyletic?
The tribe Sophoreae appears not to be monophyletic, but rather contains many smaller clades with affinities to Swartzieae pro parte, Dalbergieae, and even Podalyrieae in the case of Cadia (Doyle, 1995
; Doyle et al., 2000
; Ireland, Pennington, and Preston, 2000
). The Sophoreae tribe originally included a mix of taxa having flowers with some or all of the following plesiomorphic character states: radial symmetry, uniform petals, and free, uniform stamens. Cadia was found (Doyle, 1995
; Doyle et al., 2000
) to have the 50-kilobase chloroplast DNA inversion in common with the higher papilionoid tribes, in contrast to many Sophoreae that lack the inversion. Possession of the inversion would place Cadia either in a core Sophoreae or in Podalyrieae with three South African genera.
While Sophoreae sensu Polhill (1981)
may be obsolete, several monophyletic clades of sophoroid taxa may merit retention. One should keep in mind that certain morphological as well as developmental character states seem to be correlated with the unspecialized floral structure of the taxa included. Pollen type is essentially uniform (Ferguson, Schrire, and Sheggerson, 1994
). A particular type of endothecial thickening occurs in anthers of several genera of Sophoreae (Manning and Stirton, 1994
). Wood and pollen evidence, however, did not support Sophoreae as a monophyletic entity. Using pollen evidence, Ferguson, Schrire, and Shepperson (1994)
found four clades in Sophoreae that did not correlate well with Polhill's groups (1981, 1994)
of Sophoreae. Swartzia was used as one outgroup but consistently was included in one of the ingroup clades, based on pollen data. Elements of some Sophoreae are more similar to Swartzieae (Herendeen, 1995
), based on a morphological analysis. Analysis of information on wood features (Gasson, 1994
) suggested a nonmonophyletic Sophoreae. The Cadia group of Polhill in particular is polymorphic, and the wood of Cadia itself is unlike that of any other genera of Sophoreae. Gasson cautions that many wood characters reflect habit and environmental adaptations.
What, then, does floral ontogenetic evidence contribute to a consideration of the phylogenetic position of Cadia? Its consistently unidirectional organogenesis conforms with that of the other taxa of Sophoreae sensu Polhill (1981, 1994)
that have been documented and agrees with the great majority of other papilionoid legumes from many tribes (including an incomplete series for Calpurnia aurea in Podalyrieae; unpublished data). The radial symmetry of Cadia is viewed as a neotenous retention of the symmetry prevailing in early developmental stages of almost all papilionoid flowers (Tucker, 2001
). Its random petal aestivation is an exception to the prevailing state (descending cochleate) found in most other papilionoids and is also considered to be neotenous.
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FOOTNOTES |
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2 tucker{at}lifesci.ucsb.edu
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONLITERATURE CITED |
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Doyle J. J. 1995 DNA data and legume phylogeny: a progress report. In M. Crisp and J. J. Doyle [eds.], Advances in legume systematics. Part 7. Phylogeny, 11–30. Royal Botanic Gardens, Kew, Richmond, UK
Doyle J. J. J. A. Chappill C. D. Bailey T. Kajita 2000 Towards a comprehensive phylogeny of legumes: evidence from rbcL sequences and non-molecular data. In P. S. Herendeen and A. Bruneau [eds.], Advances in legume systematics. Part 9, 1–20. Royal Botanic Gardens, Kew, Richmond, UK
Ferguson I. K. B. D. Schrire R. Shepperson 1994 Pollen morphology of the tribe Sophoreae and relationships between subfamilies Caesalpinioideae and Papilionoideae (Leguminosae). In I. K. Ferguson and S. C. Tucker [eds.], Advances in legume systematics. Part 6. Structural botany, 58–97. Royal Botanic Gardens, Kew, Richmond, UK
Gasson P. E. 1994 Wood anatomy of the tribe Sophoreae and related Caesalpinioideae and Papilionoideae. In I. K. Ferguson and S. C. Tucker [eds.], Advances in legume systematics. Part 6. Structural botany, 165–204. Royal Botanic Gardens, Kew, Richmond, UK
Herendeen P. S. 1995 Phylogenetic relationships of the tribe Swartzieae. In M. D. Crisp and J. J. Doyle [eds.], Advances in legume systematics. Part 4. The fossil record, 123–132. Royal Botanic Gardens, Kew, Richmond, Surrey, UK
Hutchinson J. 1964 The genera of flowering plants (Angiospermae). 1. Dicotyledones. Clarendon Press, Oxford, UK
Ireland H. R. T. Pennington J. Preston 2000 Molecular systematics of the Swartzieae. In P. S. Herendeen and A. Bruneau [eds.], Advances in legume systematics. Part 9, 217–231. Royal Botanic Gardens, Kew, Richmond, UK
Klitgaard B. B. 1999 Floral ontogeny of four taxa of Dalbergieae. Plant Systematics and Evolution 219: 1-25[CrossRef][ISI]
Manning J. C. C. H. Stirton 1994 Endothecial thickenings and phylogeny of the Leguminosae. In I. K. Ferguson and S. C. Tucker [eds.], Advances in legume systematics. Part 6. Structural botany, 141–164. Royal Botanic Gardens, Kew, Richmond, UK
Pennington R. T. B. Klitgaard H. Ireland M. Lavin 2000 New insights into floral evolution of basal Papilionoideae from molecular phylogenies. In P. S. Herendeen and A. Bruneau [eds.], Advances in legume systematics. Part 9, 233–248. Royal Botanic Gardens, Kew, Richmond, UK
Pennington R. T. M. Lavin H. Ireland B. B. Klitgaard J. Preston J.-M. Hu 2001 Phylogenetic relationships of basal papilionoid legumes based upon sequences of the chloroplast trnL intron. Systematic Botany 26: 537-556[ISI]
Polhill R. M. 1981 Sophoreae. In R. M. Polhill and P. H. Raven [eds.], Advances in legume systematics. Part 1, 213–230. Royal Botanic Gardens, Kew, Richmond, UK
Polhill R. M. 1994 Complete synopsis of legume genera. In F. A. Bisby, J. Buckingham, and J. B. Harborne [eds.], Phytochemical dictionary of the Leguminosae, vol. 1, xlix–liv. Chapman and Hall, New York, New York, USA
Tucker S. C. 1984 Origin of symmetry in flowers. In R. A. White and R. C. Dickison [eds.], Contemporary problems in plant anatomy, 352–394. Academic Press, New York, New York, USA
Tucker S. C. 1985 Unidirectional organ initiation in leguminous flowers. American Journal of Botany 71: 1139-1148[CrossRef][ISI]
Tucker S. C. 1987 Floral initiation and development in legumes. In C. H. Stirton [ed.], Advances in legume systematics. Part 3, 183–239. Royal Botanic Gardens, Kew, Richmond, UK
Tucker S. C. 1989 Overlapping organ initiation and common primordia in flowers of Pisum sativum (Leguminosae: Papilionoideae). American Journal of Botany 76: 714-729[CrossRef][ISI]
Tucker S. C. 1990 Loss of floral organs in Ateleia (Leguminosae: Papilionoideae: Sophoreae). American Journal of Botany 77: 750-761[CrossRef][ISI]
Tucker S. C. 1993 Floral ontogeny in Sophoreae (Leguminosae: Papilionoideae) I. Myroxylon (Myroxylon group) and Castanospermum (Angylocalyx group). American Journal of Botany 80: 65-75
Tucker S. C. 1994 Floral ontogeny in Sophoreae (Leguminosae: Papilionoideae): II. Sophora sensu lato (Sophora group). American Journal of Botany 81: 368-380[CrossRef][ISI]
Tucker S. C. 1997 Floral evolution, development, and convergence: the hierarchical-significance hypothesis. International Journal of Plant Sciences 158: (Supplement 6) S143-S161[CrossRef]
Tucker S. C. 2001 Floral development of Swartzieae vs. higher Papilionoideae: Multiple origins, reversions, or neoteny?. Fourth International Legume Conference, Canberra, Australia, 2–6 July 2001. Abstracts, 89–90. Australian National University, Canberra, Australia
Tucker S. C. C. H. Stirton 1991 Development of the cymose inflorescence, cupulum and flower of Psoralea pinnata (Leguminosae: Papilionoideae). Botanical Journal of the Linnean Society 106: 209-227
Van der Maesen L. J. G. 1970 Primitiae Abricanae VIII. A revision of the genus Cadia Forskae (Caes.) and some remarks regarding Dicraeopetalum Harms (Pap.) and Platycelyphium (Harms) (Pap). Acta Botanica Neerlandica 19: 227-248[ISI]
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