New taxa and new combinations in Hawaiian Bidens (Asteraceae)

p. [1]-16: ill.; 23 cm.In the course of our investigation of the genetics of adaptive radiation and evolution of Bidens in the Hawaiian Islands, it has been necessary to revise the group taxonomically. Here we describe four new subspecies and make three new combinations at the rank of subspecies. Bidens sandvicensis ssp. confusa Nagata & Ganders, B. hillebrandiana ssp. polycephala Nagata & Ganders, B. micrantha ssp. kalealaha Nagata & Ganders, and B. forbesii ssp. kahiliensis Ganders & Nagata are described as new. Bidens campylotheca ssp. pentamera (Sherff) Ganders & Nagata, B. menziesii ssp. filijormis (Sherff) Ganders & Nagata, and B. micrantha ssp. ctenophylla (Sherff) Nagata & Ganders are published as new combinations at subspecific rank. A key to all taxa of Bidens in the Hawaiian Islands is provided. It includes introduced taxa that have been collected in the islands in the last 80 years

Relationships and floral biology of Bidens cosmoides (Asteraceae)

p. [23]-32: ill.; 23 cm.Bidens cosmoides, in the monotypic section Degeneria, is a morphologically unique species endemic to Kaua'i. Contrary to previous reports it will hybridize successfully with other Hawaiian species of Bidens, all in section Campylotheca. All Hawaiian species of Bidens are interfertile, suggesting that they are the products of adaptive radiation from a single ancestral introduction rather than two separate introductions and lineages as previously postulated. The elongated styles of B. cosmoides, exserted 20-30 mm beyond the corollas, that present pollen on the style tips, are unique in the genus. Flowers produce more than 30 times as much nectar by volume than do other Hawaiian species of Bidens, but the sugar concentration of the nectar is only half that of other species (30% vs. 60%). These unique floral features appear to represent adaptations to pollination by birds, although pollination of B. cosmoides has not yet been observed in nature

Microsporogenesis in male-sterile and hermaphroditic plants of nine gynodioecious taxa of Hawaiian bidens (Asteraceae)

Microsporogenesis was investigated in hermaphroditic and male-sterile plants in nine gynodioecious taxa of Hawaiian Bidens. Normal microsporogenesis in hermaphrodites and the onset of abortion in male steriles were similar in all taxa and in a hybrid between two gynodioecious species. The early abnormal vacuolation of tapetal cells is the first visible evidence leading to premeiotic abortion of microsporogenesis in male steriles. The sporogenous cells disintegrate rapidly after the vacuolation of the tapetum, resulting in a shrunken, indehiscent anther which is composed of only the epidermal layer with some remnant cells of the endothecium and the connective at anthesis. In hermaphrodites, the tapetal cklls remain dense and undergo karyokinesis to become binucleate during meiosis I. The tapetum becomes plasmodia1 after microspores are released from tetrads and gradually disappears during pollen formation. The genetic factor($ which cause the abortion act with remarkable precision and consistency in all taxa investigated. This suggests that gynodioecy in all Hawaiian Bidens is homologous and the establishment of male sterility in Hawaiian Bidens occurred only once. The spread of the genetic male-sterile factor(s) may be the result of adaptive radiation of the original gynodioecious species or natural interspecific hybridization.link_to_subscribed_fulltex

HETEROSTYLY, HOMOSTYLY, AND FECUNDITY IN AMSINCKIA SPECTABILIS (BORAGINACEAE)

Volume: 23Start Page: 56End Page: 6