Systematic anatomy of Erythroxylum P. Browne: Practical and evolutionary implications for the cultivated cocas

Abstract

Preliminary study of the pantropical Erythroxylaceae indicates that anatomical features can provide valuable insight into the generic, infra-generic and specific affinities of unidentified specimens. Combinations of qualitative and quantitative anatomical data are most reliable when considered in conjunction with relevant ecological and plant morphological data. Extreme caution is advised in such taxonomic applications due to the intergrading patterns of anatomical variation exhibited within the family. Careful consideration must be given to the potential influence on anatomy of factors such as plant age, habit, leaf morphology and environmental conditions. Although a few species of Erythroxylum are identifiable solely on the basis of unique wood anatomical features, the majority of species can be identified only through a combination of morphological and vegetative anatomical features. Closely related species and species of similar habitats are often very similar in their wood and leaf structure. Anatomical differences are more subtle among the cultivated cocas and their closest neotropical relatives than among most taxa of Erythroxylaceae. A typological concept of foliar venation patterns among the cultivated cocas permits the varietal identification of isolated coca leaves. Several neotropical relatives of the cultivated cocas represent potential adulterants in commercial samples of coca leaf as a result of their striking similarity to genuine coca in leaf form, venation and anatomy. Due to the broad and overlapping range of leaf structural variation exhibited among the cultivated cocas and their nearest relatives, identifications of isolated leaves or leaf fragments are ill-advised in the absence of relevant ecological data. Patterns of wood and leaf anatomical variation within the Erythroxylaceae are most readily explicable as the result of evolutionary diversification in plant habit, leaf size, form and relative duration. Significant correlations among wood and leaf structure reveal various “adaptive strategies” among species of Erythroxylaceae. Redundant patterns of structural evolution, evident among the different species and genera of Erythroxylaceae, help to elucidate the probable evolutionary origins of the cultivated cocas. Comparative anatomical data support the hypothesis that Bolivian coca ( E. coca) represents the most primitive of the cultivated cocas. The Colombian and Trujillo varieties of coca ( E. novogranatense) appear to have been derived from a Bolivian-like ancestral coca as a result of long-term cultivation, geographic isolation and human selection for increased flavor, palatability and drought resistance.