ICKERT-BOND, STEFANIE, M. Department of Plant Biology, Arizona State University, Tempe, AZ 85287-1601. - Micromorphological and cytological patterns among New World species of Ephedra L. (Ephedraceae).
As part of an ongoing systematic study of New World Ephedra, 29
taxa were sampled for micromorphological, cytological, and ovule
ontogenetic variation. Ephedra grows as dioecious
much-branched shrubs, climbers or trees with small opposite or whorled
scale- to needle-like leaves in arid regions of the New and Old World.
Species are characterized by ovulate strobili with dry membranous,
winged or fleshy bracts; lance pyriform to ovoid seeds;
microsporangiate strobili with inaperturate, non-saccate, polyplicate
pollen; and a base chromosome number x = 7. A combination of newly
recognized and reevaluated features of potential taxonomic value
includes: micromorphology of stem and seed cuticle, leaf venation,
tubillus variation and features of ovule ontogeny. Stomata of
Ephedra are haplocheilic, monocyclic and tetracytic and occur
in furrows, which alternate with non-stomatiferous bands. Species
vary in stomatal opening shape, number of stomatal rows per furrow,
epidermal cell shape, position of cuticular flanges, and shape of
papillae. Seed coat variation exhibits three distinct types: 1)
striate and papillate, 2) striate, and 3) striate and reticulate.
Leaf venation patterns may be bi- or trifasciculate. Phyllotaxy
determines the number of ovules per strobilus, while a reduction in
ovule number has also taken place in some decussate (e.g., E.
antisyphilitica) and trimerous (e.g., E.
trifurca) taxa. Natural interspecific hybridization and
polyploidization are thought to play a role in the evolution of New
World ephedras. Cuticular characters confirm the position and
parentage of the two interspecific hybrids, E. ×
arenicola and E. × intermixta as described by H.
C. Cutler. Chromosome numbers are available for 15 species. Of the
New World taxa examined, 40 % are diploid, 13.3 % are polyploid and
46.7 % are both diploid and polyploid. These patterns are further
tested against O. Stapf's long-standing classification system.
Key words: cytology, Ephedra, micromorphology, New World species, systematics