Pillwort Name Change - No Bitter Pill To Swallow!
Pilularia is a small genus of 5-6 species scattered through Europe, North and South America, Africa, Australia, and New Zealand. Known as “pillworts” because of their globose sporocarps (capsules bearing 2-4 soral compartments and which are held on short “pedicels” near the base of the plant); pillworts are aquatic ferns which inhabit the muddy margins of lakes, ponds and rivers. Pillworts scarcely resemble the “typical” fern of popular imagination because their leaves are filiform. It is only when the young emerging leaves are examined that the circinate vernation typical of ferns becomes apparent.Traditionally New Zealand has one endemic species, P. novae-zelandiae, which was described by Thomas Kirk in 1877 from specimens gathered from Lake Whangape in the Huntly Basin. Its claim to species status has always been dubious and in 1989 New Zealand botanists Mark Large and John Braggins suggested that P. novae-zelandiae was probably conspecific with the Australian P. novae-hollandiae, even going so far as to suggest that these two species could be merged with the North American P. americana.
In a recent issue of the Botanical Journal of the Linnean Society American botanists (Nagalingum et al. (2008)) based on molecular evidence obtained from three coding plastid genes and three non-coding plastid regions have formally merged P. novae-zelandiae with the Australian P. novae-hollandiae. However, while admitting that there is very little “morphologically speaking” to retain their recircumscribed P. novae-hollandiae as a species distinct from P. americana, they argue that as both species are sister to each other, geographically highly disjunct, and because there is some sequence divergence between them (and indeed partitioning between eastern and western U.S.A. populations of P. americana), they prefer to maintain these two pillworts as separate species for the time being. Further, they remain unclear over the status of the South American species P. mandani (not included in their study), and also of the African plants that are currently referred to P. americana but which morphologically resemble better P. novae-hollandiae.
Reference
Nagalingum, N.S.; Nowak, M.D.; Pryer, K.M. 2008: Assessing phylogenetic relationships in extant heterosporous ferns (Salviniales), with a focus on Pilularia and Salvinia. Botanical Journal of the Linnean Society 157: 673-685.
Peter J. de Lange
Posted: 20/11/2008