A Revision of the Genus Plectocephalus in Ethiopia .
No Thumbnail Available
Date
1991-06
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Addis Ababa,University
Abstract
A systematic study of Plectocephalus varians (A.Rich.) C.Jeffrey ex Cuf. was
conducted with an objective of obtaining data that will contribute to rts relation with
other members of the genus and to the related genus Centaurea L. Special emphasis
was given to characters of generic value. Representative specimens of the fonowing
taxa from Latin America were studied: Plectocephalus amerjcanus Nuttal, P. chilensis
Hook & Arnott, Centaurea floccosa Hook & Arnott, C. bulbosa Hook & Arnott, C.
atacamensis (Reiche) Johnston, C. tweediei Hook & Arnott, C. rothrockii Greenm.
and C. cachlnalensis Phil. A~hough widely distributed in Ethiopia, the different
populations of P. varians are found to constitute a single taxonomic species hence
authenticating the previously established synonymy by Jeffrey (1968).
P. varians is also found to be strikingly different from any known taxon of
Centaurea in Ethiopia.Based on data from morphology, anatomy and palynology,
two ecologically differentiated populations of P. varians are recognized: grassland and
forest populations. The grassland populations differ from forest populations in the
degree of the presence of indumentum. They tend to have a higher degree of
hairiness compared to forest populations. A high or low amount of hair reflects
.
xeromorphic or mesic conditions. respectively.
Forest populations tend to have dark-green broad and large leaves with
prominent brochidodromous venation, whereas grassland populations have small
shiny, light green leaves with inconspicuous venation. In the forest populations
studied, stem anatomy revealed presence of a, hollow pith, but in the grassland
populations, the prth is filled wrth parenchymatous cells. The significance of this is
associated with either xeromorphic or mesic conditions. In grassland populations, the
ray florets are entirely purple, but forest populations tend to have yellow or mauve
ligulate flowers. The significance of this is not clear.
Description
Keywords
A Revisi.o n of the Genus Plectocephalus