THE MICROMORPHOLOGIES OF SEED COATS AND PETAL TRICHOMES OF THE TAXA OF VIOLA SUBSECT. BOREALI-AMERICANAE (VIOLACEAE) AND THEIR UTILITY IN DISCERNING ORTHOSPECIES FROM HYBRIDS

Gil-ad, N. L. (University of Michigan Herbarium, North University Buil ding, Ann Arbor, MI 48109-1057, U.S.A.). The micromorphologies of seed coats and petal trichomes of the taxa of Viola subsect. Boreali-Ameri canae (Violaceae) and their utility in discerning orthospecies from hy brids. Brittonia 50: 91-121. 1998.-Viola subsect. Boreali-Americanae, confined to North America including northern Mexico, has long been con sidered one of the most taxonomically difficult temperate groups of th e angiosperms. Hybridization, followed in some localities by introgres sion, has made it difficult for systematists to discern the ''core'' s pe cies by using only standard macromorphological characters. Analyses that employed scanning electron microscopy (SEM) of seed coats and pe tal trichomes generated new characters. SEM of the surface of seeds of each of the orthospecies revealed a suite of primary and secondary sc ulpture characters unique to each species that are correlated with a s uite of macromorphological characters. In a number of species, SEM of petal trichomes provided additional unique characters. SEM of the surf ace of seed coals enabled, also, the identification of instances of hy bridization by revealing blends of structures of the primary and secon dary sculpture typical of different orthospecies and instances of puta tive introgression by revealing deviations in surface structures from those typical of orthospecies. A procedure based on iterative examinat ions of macromorphology and micromorphology, which was developed in th is research, enabled the discernment of hybrids and putative introgres sants. Combining the micromorphological and macromorphological data wi th ecological and phytogeographical data enabled the delimitation of s ixteen orthospecies.