BOTANICAL MUSEUM LEAFLETS VoL. 26, No. 5 
May 30, 1978 
CHROMOSOME NUMBERS IN NEOTROPICAL 
ERYTHROXYLUM (ERYTHROXYLACEAE) 
T. PLOWMAN !, L. RUDENBERG2, AND C.W. GREENE? 
The genus Erythroxylum includes some 200 species, the 
great majority of which are found in the American tropics. 
Within this genus are found several economically important 
plants, most notably E. Coca Lam. and FE. novogranatense 
(Morris) Hieron. These two closely related species native to 
South America are extensively cultivated as the sole source of 
the alkaloid cocaine. Numerous cultivars and local races of 
these species occur in the Amazon and Andes, the result of at 
least 6000 years of coca cultivation. The variation and evolu- 
tion of coca under domestication has been little studied in 
recent years and little is known about the cytogenetics and 
breeding relationships of this important crop. 
As part of a multidisciplinary project on coca, we have 
conducted a preliminary cytological study on Erythroxylum 
species. Until now, there have been no published chromosome 
counts with voucher specimens of any neotropical Erythroxy- 
lum; nor are any vouchered counts known for the cultivated 
species. Species of Erythroxylum are notoriously difficult to 
distinguish morphologically, and much confusion exists in the 
taxonomic placement of many species. It is therefore essential 
that herbarium vouchers accompany all chromosome studies 
and that chemical analyses carried out on the genus to insure 
present and future identifications. 
Five chromosome counts of Erythroxylum species have been 
published in the past. These are summarized in Table One. 
Only one of these counts (E. Kunthianum Wall.) bears a 
voucher specimen. The correct identity of the two plants de- 
termined as E. Coca is especially open to question. Several 
'Botanical Museum of Harvard University. 
2Gray Herbarium, Harvard University. 
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