Some Like It Cold (Taxon of the Week: Saccogynidium vasculosum)

I haven't introduced the Taxon of the Week post with a Name the Bug challenge this week because (a) even I'm not evil enough to make you try and identify liverworts, and (b) I haven't been able to find any illustrations of the specific liverwort concerned. The figures below from Gao et al. (2001) show other species in the same genus from China:



Leafy liverworts are small plants that are superficially similar in appearance to mosses. Like mosses, they grow in moist localities and lack well-developed supporting vascular tissue. Leafy liverworts can often be distinguished from mosses by having a different arrangement of leaves (liverwort leaves often grow in lateral rows, moss leaves in spirals), lacking a median vein in the leaf and potentially having teeth or lobes on the edge of the leaf. Liverworts also have different reproductive structures from mosses; instead of opening with a cap, liverwort spore capsules usually split down the sides.

Saccogynidium vasculosum is a species of liverwort restricted to the Falkland Islands and the very southernmost part of South America (Engel, 1990; Frey & Schaumann, 2002). Earlier authors referred to it as Lophocolea vasculosa but this was due to confusion with a different species, L. elata, from which it can be distinguished by the presence of small papillae (bumps) covering the leaves, a feature of the genus Saccogynidium (Engel, 1978). Saccogynidium is also distinguished from related genera by producing the female reproductive organs inside a fleshy protective covering called a marsupium (one is shown in the lower part of the figure above). Saccogynidium vasculosum is distinguished from other species in the genus by having finer papillae on the leaves, and having the tips of the leaves narrowly rounded rather than two-pointed.

Whar's really notable about Saccogynidium is its distribution (Schuster, 1972). As well as S. vasculosum, the Falkland Islands are home to S. australe, a species also found in New Zealand. Other species are found in Tasmania and south-east Asia. Interesting questions could be asked whether the current distribution of Saccogynidium is due to Gondwanan ancestry (in which case the disjoint distribution of S. australe might argue for incredibly slow rates of evolution) or to more recent dispersal, something some authors seem to have dismissed out of hand.

REFERENCES

Engel, J. J. 1978. A taxonomic and phytogeographic study of Brunswick Peninsula (Strait of Magellan) Hepaticae and Anthocerotae. Fieldiana: Botany 41.

Engel, J. J. 1990. Falkland Islands (Islas Malvinas) Hepaticae and Anthocerotophyta: a taxonomic and phytogeographic study. Fieldiana: Botany, new series 25.

Frey, W., & F. Schaumann. 2002. Records of rare southern South American bryophytes. Studies in austral temperate rain forest bryophytes 18. Nova Hedwigia 74 (3-4): 533-543.

Gao, C., T. Cao & M.-J. Lai. 2001. The genus Saccogynidium (Geocalycaceae, Hepaticae) in China. Bryologist 104 (1): 126-129.

Schuster, R. M. 1972. Continental movements, "Wallace's Line" and Indomalayan-Australasian dispersal of land plants: some eclectic concepts. Botanical Review 38 (1): 3-86.