New Zealand Journal of Botany abstracts

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Chromosome numbers for the New Zealand species of Psilotum and Tmesipteris, and the phylogenetic relationships of the Psilotales

P. J. BROWNSEY

National Museum of New Zealand
Private Bag, Wellington, New Zealand

J. D. LOVIS

Department of Plant and Microbial Sciences
University of Canterbury, Christchurch
New Zealand

Abstract Chromosome counts of n = 104 are reported for New Zealand populations of Psilotum nudum, Tmesipteris elongata, T. lanceolata, T. sig- matifolia and T. tannensis. These results confirm that Psilotum and Tmesipteris share the same base number, x = 52, and show that the New Zealand species of Tmesipteris are all tetraploid compared with Australian species which include both tetra- ploids and octoploids. A difference in ploidy sup- ports the morphological distinction between the New Zealand T. tannensis and the closely related Australian T. billardierei. The recent reinstatement of Psilotum heterocar- pum Colenso as a distinct species is shown to be based on a misconception. Cytological observations relevant to the hypoth- esis that the Psilotaceae are related to primitive members of the Filicales are discussed. No sub- stantial cytological evidence can be found to sup- port this concept which is also contrary to phytochemical and other evidence. The origin and relationships of the Psilotales remain open questions. It is still possible that, though not belonging to the Filicales, they are nevertheless archaic ferns, constituting an inde- pendent sub-class of the Filicopsida, but recent morphological evidence makes a direct relation- ship with rhyniophytes more likely. In this case it is probable that Psilotum is the less modified of the two extant genera. It is considered preferable at the present time to retain a system of classifi- cation whereby the four main groups of living pter- idophytesó psilopsids, lycopsids, sphenopsids, and fernsó are treated as independent groups of equal status. The question as to whether Psilotum and Tmesipteris should be placed in the same or separ- ate families is also discussed.

Keywords fern allies; Psilotales; Psilotaceae; Tmesipteridaceae; Psilotum; Tmesipteris; Psilotum nudum; Tmesipteris elongata; Tmesipteris lanceo- lata; Tmesipteris sigmatifolia; Tmesipteris tannen- sis; chromosome counts; cytotaxonomy; phylogeny; phytochemistry; New Zealand flora

Received 11 June 1986; accepted 8 August 1986
New Zealand Journal of Botany, 1987, Vol. 25 : 439-454
0028-825X/87/2503-0439$2.50/0 © Crown copyright 1987

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