Lanterna Rally

Author: Frank Almeda

Publisher: Amer Society of Plant Taxonomists

Published: 2011

Total Pages: 101

ISBN-13: 9780912861937

This study represents the first attempt to evaluate generic and species limits in the South American genus Siphanthera by incorporating new information from macromorphology, pollen and seed micromorphology, chromosome cytology, a cladistic analysis, and distributional information. Available data provide a rationale for recognizing Siphanthera as a monophyletic genus of fifteen species with a bicentric distribution centered in the Brazilian Planalto, and the Guayana Highlands and contiguous areas. The monotypic genus Farringtonia has been merged with Siphanthera during this study and two new species are proposed here, S. todziae from the Amazon Basin and S. wurdackii from the Brazilian Planalto. The recent assignment of Siphanthera to the broadly defined tribe Melastomeae is called into question pending the results of a forthcoming family-wide multi-gene phylogenetic analysis. An evaluation of taxonomic characters used to recognize previous infrageneric groups has led to the abandonment of a formal sectional classification of the genus. Some major evolutionary trends in Siphanthera include: change from a perennial to an annual life cycle; change in foliar venation from basal acrodromous to loss of secondaries in one direction and change in the prominence of secondary veins and their pattern of divergence from the primary vein in another direction; reduction in inflorescence complexity from branched compound dichasia to congested capituliform inflorescences or few-flowered or solitary flowered inflorescences; change in petal shape from obovate with a rounded to acute base to more or less rotund petals with a clawed base; reduction in stamen number from eight fertile stamens to four fertile stamens; change in anther shape from elongate and subulate or rostrate with a small apical pore to ovoid or subrotund with a broad ventrally or dorsally inclined apical pore; and modification of capsule shape from essentially globose with a rounded apex to laterally compressed with a bilobed or notched apex. Species constituting the first diverging lineage in our cladogram suggest a possible Brazilian Planalto origin for the genus. Pathways to northward migration were opened via large areas of continuous savanna vegetation across the Amazon Basin that connected the Brazilian and Guayana Shields during climatic fluctuations of the Pleistocene. In a less likely alternative, the distribution of Siphanthera can be accounted for by vicariance of a widespread ancestor that spanned the Brazilian and Guayana Shields. In this scenario, the taxa that branch off from the first diverging clade in our phylogenetic tree could represent a geographic sequence of differentiation from the widespread ancestor and not a series of dispersal events. Present-day rain forest dominance of the Amazon Basin with its few and scattered savanna islands has largely isolated northern and southern populations of Siphanthera and appears to explain the prevailing bicentric concentration of species on the South American continent (publisher's description.