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Systematics and reproductive biology of the central american species of the aphelandra pulcherrima complex acanthaceae


Annals of the Missouri Botanical Garden 71(1): 104-165
Systematics and reproductive biology of the central american species of the aphelandra pulcherrima complex acanthaceae
Aphelandra (Acanthaceae) is a neotropical genus of about 170 spp. of herbs, shrubs and small trees. The A. pulcherrima complex is a monophyletic group of about 40 spp. distinguished by the presence of bracteal nectaries and a unique corolla morphology. Thirteen Central American species belonging to this complex are recognized based on herbarium, field, and greenhouse studies; pollen morphology; and artificial hybridizations. The genus Aphelandra and the A. pulcherrima complex probably originated in South America. Central American species have evolved from South American or intermediate Central American ancestors. The species treated here are diffusely branched shrubs or sparsely branched, monocaulous plants. They are found in primary forest to disturbed secondary and edge habitats, and from low to middle elevations. All species produce odorless flowers that last a single day, produce copious, rather dilute nectar, and are hummingbird pollinated. All but A. deppeana are pollinated by large hermit hummingbirds (Trochilidae: Phaethorninae) or hermit-like species. The long, decurved bills and traplining foraging habits of these birds correspond to the floral morphology and spatial distribution of the plants. Chromosome data are not systematically useful within the group studied. All 12 spp. for which counts were obtained have n = 14 chromosomes. The 13 spp. are variable palynologically, showing 3 distinct pollen types, as well as significant variability in pollen size (length and width). Pollen characters resolve all but 2 spp. and provide evidence for patterns of phylogenetic relationships among the species. Although hybrids between many species pairs can be readily synthesized, hybrids in nature are rare. Four isolating mechanisms in addition to allopatry and intersterility are identified as potentially important among Central American Aphelandras. The paucity of naturally occurring hybrids is in most cases due to more than 1 type of barrier. Putative hybrids between A. sinclairiana and A. gracilis, and between A. sinclairiana and A. golfodulcensis were found in the field. Artificial disturbance has apparently been important in creating situations favorable for hybridization between at least 1 of these pairs of species. Phylogenetic analysis identifies 2 main lineages within the group: Group I (A. terryae, A. sinclairiana, A. storkii, A. gracilis, A. golfodulcensis, A. panamensis, and A. deppeana) and Group II (A. lingua-bovis, A. leonardii, A. laxa, A. campanensis, A. hartwegiana, and A. darienensis). These results are in accord with data from artificial hybridizations, except that phylogenetic analysis indicates that the species of Group II are as closely interrelated as those of Group I, whereas crossability indices suggest that these species are much more distantly related. Genetic incompatibility may be an important barrier to interbreeding between species of Group II such that the results of artificial hybridizations do not provide reliable estimates of the degree of relationship among these species.

Accession: 006574504

DOI: 10.2307/2399058

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