Bibliographic Detail

Casanova, M.T., Winton, M.D. de, Karol, K.G. & Clayton, J.S., 2007

Reference:
Casanova, M.T., Winton, M.D. de, Karol, K.G. & Clayton, J.S. (2007). Nitella hookeri A.Braun (Characeae, Charophyceae) in New Zealand and Australia: implications for endemism, speciation and biogeography. Charophytes 1(1): 2-18, 7 figs.

Publication Date:
2007

Abstract:
Members of the Nitella hookeri A. Braun complex have been recorded from New Zealand, Tasmania, Australia and Kerguelen Island. In a previous revision, three varieties of N. hookeri were delineated: lax plants (allocated to the type variety); smaller plants with numerous compact heads (var. tricellularis); and striking ones with distinctive fertile spikes (var. masonae). Workers in charophyte ecology found it difficult to distinguish among these taxa, and found additional specimens that did not conform to any of the varieties delineated. Preliminary studies revealed that Australian specimens were consistently different to those found in New Zealand. Therefore an experimental analysis of the morphology of specimens of N. hookeri was undertaken to determine the taxonomic status of entities within this group, describe the taxa that resulted from the analysis, and highlight the diagnostic characteristics. This analysis supports the reinstatement of N. tricellularis as a separate species, elevation of varieties arthroglochin and masonae to species, and the circumscription of the new species Nitella claytonii. Revision of N. hookeri, resulting in the circumscription of N. arthroglochin, N. masonae and N. claytonii and reinstatement of the New Zealand endemic species N. tricellularis, does not support the contention that New Zealand contains a sub-set of Australian charophytes, and suggests that a critical revision of other species in New Zealand is warranted. The taxa are separated on morphological grounds, oospore wall ornamentation and chromosome numbers, and the data suggest that the group has undergone rapid radiation in New Zealand. The circumpolar distribution leads us to hypothesise that related taxa will be found in Tasmania, South Africa and South America.