OSMUNDA (OSMUNDACEAE) FROM THE TRIASSIC OF ANTARCTICA - AN EXAMPLE OFEVOLUTIONARY STASIS

Citation
Cj. Phipps et al., OSMUNDA (OSMUNDACEAE) FROM THE TRIASSIC OF ANTARCTICA - AN EXAMPLE OFEVOLUTIONARY STASIS, American journal of botany, 85(6), 1998, pp. 888-895
Citations number
34
Categorie Soggetti
Plant Sciences
Journal title
ISSN journal
00029122
Volume
85
Issue
6
Year of publication
1998
Pages
888 - 895
Database
ISI
SICI code
0002-9122(1998)85:6<888:O(FTTO>2.0.ZU;2-X
Abstract
Compressed specimens of the fern Osmunda are described from the Triass ic of the Allan Hills, Antarctica. The specimens consist of a once pin nate, deeply pinnatifid fertile frond as well as several sterile speci mens. Six pinnae are present on the partial fertile rachis, with two s terile pinnae above four fertile pinnae. Both sterile and fertile spec imens are virtually identical to the modern species Osmunda claytonian a. Entire fronds are fragmentary; the longest is 21 cm in length. Ster ile pinnae are alternate and deeply pinnatifid, with slightly toothed pinnules and dichotomous venation. Fertile pinnae are 1-1.3 cm long, o nce pinnate, and lack vegetative lamina. Sporangia are clustered, each 300-375 mu m in diameter, and possess a transverse annulus 6-8 cells long; dehiscence is by a vertical slit. Fronds arise from a rhizome 4 cm long by 1 cm wide; two croziers are present on the rhizome. Two fro nd segments up to 6 cm long and three deeply pinnatifid pinnae are pre sent on the uppermost part of one rachis. Pinnules are similar to 4 mm long and 2-3 mm wide. The presence of this Osmunda species in the Tri assic demonstrates stasis of frond morphology, both fertile and vegeta tive, for the genus.