Monographs Details: Croton
Authority: Maguire, Bassett. 1965. The Botany of the Guayana Highland. Mem. New York Bot. Gard. 12 (3): 1-285.
Family:Euphorbiaceae
Scientific Name:Croton
Discussion:This paper is the first of a series of reports planned for Euphorhiaceae obtained in the course of the Garden's explorations of Guayana. It is intended to give a systematic review of new species, plus a synopsis, relative to the area, of material publislied to date and arranged into a key. Müller of Argau's monograph of Croton of the world, based on the most minute analysis of material available at that time (1866 and 1873), was a monumental job and commends admiration; nothing similar has been done since. The number of species of Croton for the world given in DeCandolle's Prodromus was 453. Today the number of Croton of the world stands around 1000, three-fourths of which are from the N e w World, about 470 from South America, 280 from the rest. A n d South America with its 470 described species is still the least explored continent of the world. Six of the species described herein are closely related to each other and belong to the C. matourensis-gronp, and seem to be as many geographically isolated endemics. The relations of the other three are less close. With the exception of four species (C. galeopsifolia, C. cedycularis, C. staJiclianus and C. arirambe), all 25 post-Mlillerian types were examined and are either in the herbarium of The New York Botanical Garden (NY), or have been obtained on loan through the courtesy of Arnold Arboretum (A), Chicago Field Museum (F), and Utrecht ( U ). A more serious problem is faced in regard to the 28 pre-Miillerian and Miillerian types. Through fortunate circumstances. The N e w York Botanical Garden possesses 4 Spruce isotypes: C. be nth ami anus, C. paletnostigma, C. caryophyllus and C. mollis, and 10 photographs of other types {C. matourensis, C. spruceanus, C. hostmanni, C. suljincanus, C. suavis, C. cajucara, C. guayanensis, C. martii, C. amazonicus, C. umbratilis). The remaining 14 types are known to m e only from description. In all instances of pre-Miillerian and Miillerian species, actually no holotypes have been designated and a great number of syntypes will have to be examined in European herbaria, with lectotypes and neotypes yet to be designated. The present is an artificial key, but it also intends to express natural relationship so far as possible. It is thought that certain vegetative characters, such as indumentum, presence of glands at the base of blade, dissected shape and ciliate margin of stipules, bracts and calyx lobes, are more expressive of natural relationship than bisexuality of basal glomerules, or their discontinuity, or flatness versus reduplication of calyx lobes, as used by Miiller under sect. Eucroton. Shape and ornamentation of seeds are undoubtedly important taxonomically but frequently unobtainable. Because of the tentative character of the key, it appears impractical to attempt to use and redefine the old sectional nomenclature.