Taxonomic studies on Brazilian species of Cordia L. (Boraginaceae)

Abstract

The family Boraginaceae s.l., to which the genus Cordia belongs, comprises some 100 genera and includes ca. 2000 species (Willis, 1973; Cronquist, 1983) with a more or less cosmopolitan distribution. Bentham & Hooker (1876) divided the Boraginaceae in to four tribes based primarily on the characteristics of the style and ovary: (1) Cordieae (style terminal, four-branched with each arm terminating in a clavate or capitate stigma; ovary unlobed); (2) Ehretieae (style terminal or lateral, stigma 4-lobed or bifid); (3) Heliotropieae (style terminal or lateral, stigma 4-lobed, elongate with a subapical depression, ovary unlobed); (4) Borageae (style gynobasic, stigma truncate or capitate, ovary distinctly 4-lobed). Subsequently, these tribes were elevated to the category of subfamily by Gürke (1897, in Engler & Prantl, Die Natürlichen Pflanzenfamilien): (1) Cordioideae, (2) Ehretioideae: (3) Heliotropoideae and (4) Boraginoideae. This treatment of the family Boraginaceae was followed by Rendle (1925), Lawrence (1951) and Cronquist (1983). Hutchinson (1959), combined Cordioideae and Ehretioideae in a distinct (largely woody) family Ehretiaceae with the remaining subfamilies comprising the (largely herbaceous) Boraginaceae s.str. The treatment by Gürke (1897), however, has been more widely accepted, with the genus Cordia aligned with Patagonula and Auxema under the subfamily Cordioideae. The genus Cordia is particularly well represented in the large area of South America delimited by the Federal Republic of Brazil (some 65 species are recognised in the present revision, i.e. ca. one quarter of the total number of species in the whole genus). The treatment of Cordia by Fresenius (1857) for von Martius' Flora Brasiliensis was unfortunate in being based in large part on a rather infelicitous view of the genus by De Candolle (1845) so that although this has been the standard taxonomic work for Cordia in Brazil, it suffers from many deficiencies. Of great value are the taxonomic studies by Johnston (1930-1956) which provided lucid accounts of the infrageneric taxa and species limits (see sect. II for detailed discussion). However, these accounts by Johnston are based on regional areas and extended over a period of 2S years during which this author changed his view of the taxonomy of generic, sectional and specific delimitations. The revision by Johnston (1930) consists the last treatment of the genus for part of Brazil, and thus there is no modern taxonomic account for Cordia for this country. It is this deficiency which the present study attempts to remedy. The present revision is restricted to the Brazilian species of Cordia, but a view of the genus as a whole, in particular the status of infrageneric categories has also been evaluated. Accompanying a formal revision based on external morphology, a palynological study of a number of species of the genus is provided, and also a discussion of the reproductive biology of some species, particularly with regard to the occurrence of heterostyly. The entire genus Cordia presents many interesting aspects such as its diverse morphological features of habit, inflorescence pattern, flowers and fruits; the reproductive biology with heterostyly presumably evolving towards dioecy in many species and perhaps a high level of polyploidy.