Cactus Correction Conundrum

R.S. Wallace S1.RSW at ISUMVS.IASTATE.EDU
Tue Sep 7 16:09:39 EST 1993


TO:  CRAZY CACTUS CONTEMPLATORS
FROM:  Robert S. Wallace, Dept. of Botany, Iowa State Univ.
Subject:  Response to Ellmore, Biology, Tufts

Note that Ellmore correctly states that the genus Pereskia is indeed
a leafy cactus, with true leaves arising from the areoles of the
stem (moreover the other genus of Subfamily Pereskioideae,
Maihuenia, which is endemic to southern South America, also has true
leaves and non-arillate seeds).  In addition to this, nearly all
members of Subfamily Opuntioideae have (normally ephemeral) true
leaves.  My comments to "VAS" were to potentially aid in the
*correct* identification of what the plant is question is.
     If Ellmore had read the original description in the original
posting, it would be clear that with a plant having stems triangular
in cross section with spines only at the ridges, it is obvious that
no member of the Pereskioideae or Opuntioideae would fit in this
description.  Within the Subfamily Cactoideae, very few of these
taxa have leaves that are visible.  Since the original description
included centimeter measurements of leaves, it can only be concluded
(if these in fact are leaves) that the plant in question may not
really be a cactus, but a plant of Euphorbia, which is often
confused with cacti, because of its convergent morphology.
     I stand "corrected" in sense for not accurately placing "true
leaves" in the right context of my last posting.  ALL cacti have
leaves, no matter how microscopic or macroscopic; however practical
description to assist identification took precedence over precise
terminological accuracy.  Thanks for the memories..............

Sincerely,

Robert S. Wallace
Department of Botany
Iowa State University

Internet: s1.rsw at isumvs.iastate.edu



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