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Bornman, C.H. 1977. Welwitschia mirabilis: structural and functional anomalies. Madoqua, 10(1): 21-31


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Welwitschia mirabilis: structural and functional anomalies.

Summary / Notes:

Welwitschia mirabilis displays certain morphological and physiological features that may be regarded as either gymnospermous or angiospermous. It appears to be a C3/CAM plant, the CAM pathway of photosynthetic CO2 fixation probably having evolved in order to adapt to the extremes of the Namib Desert habitat. The apparent ability to switch from C3 to CAM suggests that Welwitschia originated during a time when more favourable climatic conditions prevailed. And this raises a question: is the Namib Desert not a comparatively young desert? Seen in toto, the many anomalies (eg. gymnospermlike sieve cells, megastrobili, nakedseededness; angiospermlike vessel elements, microstrobili, CAM, mode of chlorophyll formation) confirm the viewpoint that Welwitschia represents an extremeIy specialized endpoint in pIant evolution and that it is not closely related to any extant gymnosperm or angiosperm. Keywords: Aborted pistil, Acephalous plant, Coastal fog, Coastal lichen desert, EcologicaI adaptations, Ecological adaptations, Grassland savanna, Grassland scrub-desert, Longest-lived leaf, Monogeneric, Monospecific, Namib Desert endemic, Nutritive gametophytic tissue, Phenotypic plasticity, Photosynthetic pathways, Pseudo-hermaphroditic flower, Taxonomic status, Transfusion tracheids, Trilocular anther, Tritiated water.

Year: 1977

Type: Journal Article

Origin: DRFN DLIB

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