A MATING SYSTEM CONUNDRUM - HYBRIDIZATION IN APOCYNUM (APOCYNACEAE)

Citation
Sa. Johnson et al., A MATING SYSTEM CONUNDRUM - HYBRIDIZATION IN APOCYNUM (APOCYNACEAE), American journal of botany, 85(9), 1998, pp. 1316-1323
Citations number
26
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Plant Sciences
Journal title
ISSN journal
0002-9122
Volume
85
Issue
9
Year of publication
1998
Pages
1316 - 1323
Database
ISI
SICI code
0002-9122(1998)85:9<1316:AMSC-H>2.0.ZU;2-Z
Abstract
Based upon an intermediate morphology, Apocynum x-floribundum Greene h as long been considered a hybrid involving A. androsaemifolium and A. cannabinum. The floral morphology in this genus, however, appears to p rohibit bath import and export of pollen, and observations of numerous insect visitors reveal that pollen is not routinely carried from flow er to flower Furthermore, reproductive success as measured by fruit se t is very low in most populations. Hybridization was thus called into question, with allozyme evidence used to test the hypothesis of a hybr id origin for A. x-floribundum. Six diagnostic loci, as well as two lo ci exhibiting highly disparate allele frequencies, were resolved for e ach parent. All examined populations of A. x-floribundum were heterozy gous at these loci, thus supporting the hypothesis of hybridization. E vidence from additional loci indicated that all populations tend to be strongly clonal. Observed heterozygosity was very low in the parental species, suggesting a history of inbreeding or a severe bottleneck. T here was no support for earlier assumptions that some intermediates ar e derived from backcrosses or ''secondary hybrids.'' Statistical analy ses of plant height, leaf shape, petal length, sepal length, follicle length, seed length, and seed number per follicle supported these conc lusions. The persistence and vegetative spread of hybrid clones may co ntribute to the illusion that hybridization is common.