A study of the interrelationships of some Natal species of Senecio (Asteraceae/Compositae)
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Date
1984
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Abstract
This dissertation presents the results of studies of the generic concept
of Senecio and the subsequent testing of the hypothes is: that many of
the species of Senecio in Natal are congeneric with Senecio L. sensu
stricto. The sample of taxa studied consisted of 87 Natal senecios, 5
Cape heterochromous senecios and 10 non-southern African senecios,
including the type of the genus, S. vulgaris L. Also included in the
study were 5 species from taxonomically closely related genera in the
tribe Senecioneae and two senecios of uncertain taxonomic position.
The phenotype of these taxa was investigated with respect to a large
number of morphological and micromorphological characters (126) and the
data obtained were analysed neurally and numerically.
Aspects of the pollen micromorphology, of all the taxa studied, were
also investigated using the scanning electron microscope.
A review of the chemical complement of all the taxa studied.
particularly with respect to terpenes and pyrrolizidine alkaloids, was
also undertaken.
Six characters were selected as being taxonomically significant with
respect to elucidating the generic concept of Senecio. A further 31
characters and the aforementioned 6, were selected as .being
taxonomically significant with respect to elucidating the
interrelationships of the Natal senecios and all the senecios studied. The generic concept of Senecio has been re-circumscribed and the generic
status of each of the senecios studied has been tested according to this
concept of Senecio sensu Vincent. In the light of my concept of
Senecio, the following species are excluded from Senecio sensu Vincent:
S. barbertonicus Klatt, S. cissampelinus (DC.) Schultz Bipontinus,
S. fulgens (J.D. Hooker) Nicholson, S. helminthioides (Schultz
Bipontinus) Hilliard, S. hockii De Wild. & Muschl., S. medley-woodii
Hutchinson, S. radicans (L.L) Schultz Bipontinus, S. syringifolius
O.Hoffm., S. tamoides DC., S. transvaalensis Bolus and S. viminalis
Bremekamp. Senecio brevilorus Hilliard, S. seminiveus Wood & Evans and
S. tanacetopsis Hilliard are considered to be peripheral to Senecio s.
str. sensu Vincent, and are included in Senecio s. lat. sensu Vincent.
The hypothesis regarding the generic status of the Natal senecios has
been accepted, subsequent to the circumscription of Senecio s. str.
sensu Vincent.
Estimates of the phenetic affinity of all the members of Senecio sensu
stricto sensu Vincent, included in this study, have been made. The
majority of the Natal senecios, while clearly being members of Senecio
s. str. sensu Vincent, are distinct from virtually all the Cape and
non-southern African senecios studied. Many of the non-yellow (purple)
Natal senecios form clearly allied groups which are distinct from the
groups (clusters) composed of yellow senecios. The taxonomic position
of several taxa is questioned, in the light of the cluster analyses. The evidence from the palynological studies neither contradicts nor
supports the proposed infrageneric interrelationships, with respect to
the Natal members of Senecios. str. sensu Vincent. The evidence also
neither contradicts nor supports the proposed interrelationships between
the Natal, the Cape and the non-southern African members of Senecios.
str. sensu Vincent.
The terpene and pyrrolizidine chemistry of many of many of the senecios
studied is characterised by the presence of furanoeremophilanes.
Eremophilanes also occur and are particularly associated with a number
of non-yellow (purple) senecios. Pyrrolizidine alkaloids are not
ubiquitous amongst the senecios studied, while some senecios appear to
only synthesise pyrrolizidine alKaloids.
The review of the errpene and pyrrolizidine chemistry of the senecios
investigated, illustrates how our knowledge at or near the level of
analytic characters is far from complete. However, we have definitely
progressed from the synthetic level of character use. Nevertheless, the
relationships between the members of Senecios. str. sensu Vincent,
could not be evaluated in the light of the individual chemical
complement of terpenes and pyrrolizidine alkaloids, because of a lack of
information. An hypothesis of the chemical evolution within the
Senecioneae is tested with in Senecios. str. sensu Vincent .
Before any taxonomic changes are made to t he current composition of
Senecio L., the concept of Senecio L. s. str. sensu Vincent, needs to be
tested against a far wider sample of the genus.
Description
Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1984.
Keywords
Senecio., Compositae--Classification., Theses--Botany.