keys to the vascular plants of east texas - Botanical Research ...

YUCCA/AGAVACEAE
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snakebite (Verhoek 1978b). It has been speculated that the treatment “may have had some merit
since cardiac-stimulant glycosides are often found in association with saponins (Fruton &
Simmonds 1958)” (Verhoek 1978b).
YUCCA L.
YUCCA, BEAR-GRASS, SPANISH-BAYONET, SOAPWEED
Plants coarse, with one to many crowns of elongate, proportionally narrow, sessile, flaccid to
stiff and spear-like leaves, in East TX species these usually in a basal cluster or at ends of very
short to elongate trunk-like stems; flowers in terminal racemes or panicles; inflorescence bracts
wide-based, acute or acuminate, somewhat papery; flowers rather large; perianth drooping, of 6
thick, white to cream-colored, greenish, or purple-tinged segments; stamens 6; fruit a capsule or
fleshy and berry-like, either erect and dehiscent, or else drooping and indehiscent; seeds many.
AA genus of 35 to 40 species (Hess & Robbins 2002) of warm areas of North America (s
Canada to Mexico and Guatemala and some Caribbean islands—Irish & Irish 2000), particularly
the Sonoran and Chihuahuan deserts. Texas is one of two centers of diversity in the genus
(Clary & Simpson 1995). While most are dry area plants that vary from trunkless forms to
those having immense trunks, one species in the tropical forests of Chiapas in s Mexico is an
epiphyte (Irish & Irish 2000). YUCCAS were used by Native Americans as a source of food, fiber,
soap, and medicine. The spiny leaf tip was apparently used as a needle, often with the still-attached
fibers serving as thread (Churchill 1986c); 2,000 year old fiber and twine from YUCCA
have been found in Native American ruins in AZ. According to Bell and Castetter (in Webber
1953), “… yucca ranked foremost among the wild plants utilized by the inhabitants of the Southwest.
It holds this place because of the great variety of uses to which it could be put and to the
wide accessibility of this genus within the Southwest.” Fleshy fruited species such as Y. baccata
Torr., BANANA YUCCA, were used extensively as food by Native American groups including the
Navajo and Hopi of the sw U.S. (Irish & Irish 2000). During World Wars I and II, large amounts
of YUCCA were harvested in TX and NM for fiber (Webber 1953). All species are dependent on
yucca moths for pollination. If the moths are not present the plants reproduce vegetatively, and
as a result, large clonal populations are often encountered in the field (K. Clary, pers. comm.).
According to Powell (1988), “The Yucca Moth (Tegeticula = Pronuba) flies at dusk to a flower
where she climbs stamens to collect pollen and pack the pollen in a large ball-like mass under
her neck. She then visits another flower where she inserts her ovipositer [ovipositor] directly
through the ovary wall and deposits 20–30 eggs, one at a time, each directly into an ovule. She
then climbs to the stigma of the same flower and spreads the pollen, thus ensuring pollination,
subsequent fertilization, and developing seeds that provide nourishment for the moth larvae.
Each larva ultimately destroys the seed in which it grows, but there are many undamaged
seeds left in the yucca capsule.” These yucca moth–yucca pollination mutualisms are “considered
to be among the most apparent cases of coevolution between plants and animals” (Pellmyr
et al. 1996). Baker (1986), Bogler et al. (1995), Pellmyr et al. (1996, 1997), Huth and Pellmyr (2000),
and Marr et al. (2000) described some of the complexities and evolutionary implications of pollination
in Yucca. In contrast to passive pollination, this “active pollination” (defined as “cases
where specific morphological structures and behavior components exist in the pollinator for
the purpose of picking up and transporting pollen, and depositing it on stigmas”), in which a
pollinator purposely carries out pollination, is known only in yucca moths and fig wasps
(Pellmyr 1997). Morphological features in Yucca associated with moth pollination include
“white bowl-shaped flowers, thickened filaments, pollen as the primary floral reward, [and]
odor cues for oviposition in the ovaries” (Bogler et al. 1995). Joshua Tree National Park in s CA
protects Y. brevifolia Engelm., JOSHUA TREE, one of the large-trunked species (individuals can
reach 15 m tall). (Name derived from yuca, a native Haitian or Caribbean Indian name for
Manihot esculenta Crantz (Euphorbiaceae), manihot or cassava, whose roots are used for food.