BOBICH, EDWARD G.* AND PARK S. NOBEL. Department of Organismic Biology, Ecology and Evolution, University of California, Los Angeles, CA 90095-1606. - Vegetative reproduction as related to biomechanics and anatomy for cholla species in the Sonoran Desert.
Vegetative reproduction by the rooting of detached stem segments
(joints) has long been recognized for certain cholla species, but the
stem characteristics necessary to employ this reproductive strategy
have largely been ignored. In this study, four sympatric cholla
species in the northwestern Sonoran Desert, Opuntia
acanthocarpa, O. bigelovii, O. echinocarpa, and
O. ramosissima, were characterized for their ability to
reproduce vegetatively based on the following: (1) the biomechanics
and anatomy of terminal joint junctions, which determines how easily a
joint will detach from a plant; (2) the rooting ability of detached
terminal joints; and (3) field observations of clonal reproduction.
When subjected to bending moments, terminal joints of O.
bigelovii deflected the least prior to joint junction failure,
although its junctions failed under bending moments similar to those
for O. echinocarpa and O. ramosissima, whose terminal
joints were only 10% as large. The similarity in junction strength
among these three species compared to O. acanthocarpa, which
was stronger, reflected their similar cross sectional wood areas and
essentially similar anatomy of their joint junctions. Detached
terminal joints of O. bigelovii also had the greatest rooting
ability of the four taxa, followed by O. acanthocarpa, O.
echinocarpa, and O. ramosissima. In the field, only O.
bigelovii appeared to develop regularly from detached joints.
Thus, cholla vegetative reproduction via the rooting of detached
joints apparently depends on limited wood accumulation in the joint
junctions, which results in biomechanically weak junctions, and an
ability to produce adventitious roots, both of which are particularly
evident for O. bigelovii.
Key words: anatomy, biomechanics, joint junctions, joint, Opuntia, vegetative reproduction