Experimental taxonomy of oxalis section acetosellae and maianthemum

Abstract

The taxonomy distribution of Maianthemum Web. (liliaceae) and Oxalis section Acetoaellae, are discussed withreference to their variation and evolution. I n Maianthemum there are two main taxai M. dilatatum (Wood) Nels. & Macbr., confined to the Pacific region? and M.bifolitun (L.) Schmidt with a wider distribution. The latter consists of three subspecies, subspecies bifolium of Eurasia, and subspecies canadense and subspecies interius of N. America. All these have some populations or Individuals with 2n = 36, but all also have representatives with higher chromosome numbers, 2n = 54 or 2n = c72. It is not yet possible to evaluate the chromosome races taxonomically. The taxa have similar karyotypes; the chromosomes are rather large and some are satellited. The evidence suggests that the plants with 2n = 54 and 72 are autopolyploids based on 2n = 36. Hybridization experiments have produced good seeds and a few seedlings, but no hybrids have been raised to maturity; the experiments support the view of a close genetic relationship between the taxa. M.dilatatum is morphologically variable. In Asia it has been modified as a result of contact with M.bifolium;hybridization and introgression between them may have resulted in a recognised Asian variety. In Oxalis, little is known about the Asiatic taxa. Of the other northern hemisphere taxa O.acetosella L. of Eurasia and O.montana Raf. of N. America are best treated as subspecies of O.acetosella. Hybridization experiments, because of germination difficulties, have been inconclusive. O.oregana Butt, of northwest America, is distinct from O.acetosella and hybridization experiments gave empty seeds. All three taxa have similar karyotypes. Problems of phytogeography are discussed. In both genera the taxa along the Pacific coasts of N. America are different from those of C. and E.N. America, a possible indication of their early isolation from the main stock, which perhaps originated in E. Asia.