The genus Scleria Bergius (Cyperaceae) in Southern
Africa is critically examined, and the generic limits reviewed
The taxonomic position of the genus in the family is
examined. Diagnosis of the tribe Sclerieae is altered to
circumscribe Scleria as the only genus, and diagnoses of
the tribes Bisboeckelereae and Sclerieae are made.
Infrageneric limits are re-assessed and two subgenera,
Scleria and Hypoporum recognised, the relationship of
which is postulated as co-lateral, not filial. Evidence
is presented that ecological specialisation in subgenus
Hypoporum has resulted in taxa which are adapted to open,
seasonally dry, temperate habitats, whereas ecological
specialisation in subgenus Scleria has given rise to taxa
which are adapted to shady, wet, tropical and subtropical
habitats. Taxa in subgenus Hypoporum are slender, usually
narrow-leaved annuals, or perennials with annual aerial
parts, that is, they have evolved drought/cold escape
mechanisms, the annuals by completion of the life cycle
in a season, the perennials by withdrawal of food reserves
into a protected, subterranean perennating organ and
sometimes also into enlarged culm-bases. Taxa in subgenus
Scleria are more-or-less robust, usually broad-leaved
perennials, or, less often, annuals. With few exceptions
the plants are evergreen and do not manifest drought/cold
escape mechanisms. The annual species occupy tropical
habitats in areas where seasonal drought may be
experienced and it is suggested that they have acquired the annual habit as a drought-escape mechanism. The only
perennial species in subgenus Scleria in Southern Africa
which has annual aerial parts, has evolved additional
storage regioni in the swollen culm-bases. This species,
S. transvaalensis occurs at higher, more temperate
altitudes than other species in the subgenus.
The fundamental branching pattern of the inflorescence
of all species examined has been shown to be the same. It
is postulated that the pattern is modified in two ways,
namely, by progressive contraction of all or most ramuli
leading to the "glomerate-spicate" type of inflorescence
characteristic of subgenus Hypoporum, in which the bracts
are reduced, glumiform structures, and, by progressive
contraction of some ramuli and progressive elongation of
others leading to the "interrupted-paniculate" type of
inflorescence characteristic of subgenus Scleria, in
which the bracts are foliaceous. It is suggested that the
branched glomerate-spicate type of inflorescence is less
specialised than the simply glomerate-spicate
type, and that in the line with interrupted-paniculate
inflorescences, the greater the degree of elongation and
the greater the number of elongated ramuli, the more
highly specialised the inflorescence.
Evidence is put forward that the spikelet of Scleria
is a monopodial, that is, racemosely-branched structure,
and suggestions that it may be sympodial, refuted. It is postulated that unisexual spikelets in Scleria
have been derived by reduction from bisexual (androgynaeceous)
spikelets. Unisexual female spikelets are unknown in
subgenus Hypoporum which has androgynaeceous spikelets and
unisexual male spikelets. It is suggested that the higher
the ratio of androgynaeceous to male spikelets in the
inflorescence, the less specialised the inflorescence.
Unisexual male and functionally unisexual female
spikelets occur in subgenus Scleria and, rarely,
androgynaeceous spikelets. It is suggested that species
which consistently produce some androgynaeceous spikelets
are more primitive than those which consistently lack
them, and that species whose functionally female spikelets
consistently lack any vestigial male parts are more
advanced than those which have male rudiments.
The hypogynium or "disc" which is present on some
achenes is considered to be a new modification of the
stipe of the achene and not a vestigial structure,
therefore it is postulated that the type of achene
found in subgenus Hypoporum which has a trigonous stipe
lacking any distal elaboration as an hypogynium is
primitive, and that the type of achene found in subgenus
Scleria which has an obpyramidal stipe elaborated distally
as an hypogynium is derivative. It is suggested that
development of the hypogynium has attained its most
specialised level in one group of species in which this
structure serves as a flotation device. Diagnoses of sections in subgenus Scleria are based partly on differences
in morphology of the hypogynium.
It has been demonstrated that the cell-walls of the
pericarp are silicified, that the process of silification
is progressive proceeding from the apex towards the base
of the fruit, and that abscission of the fruit takes
place when silicification is complete and the vascular
supply is severed. The achenes of subgenus Hypoporum have
all cells silicified; those of subgenus Scleria have all
cells except those of the free flange(s) of the hypogynium
silicified.
Scanning electron microscopy has revealed details of
surface ornamentation of the achenes not previously known,
which provide additional diagnostic characters at species
level.
Attemptsto germinate achenes of Scleria have been
unsuccessful : the conditions required, physical and
physiological, are not understood.
Analysis of anatomical evidence, in particular those
characters seen in transverse sections of laminas and
culms, confirms that there has been specialisation along
two divergent pathways; one which has led to successful
occupation of relatively dry, temperate habitats
(subgenus Hypoporum), and the other to successful
occupation of shaded damp, and open aquatic, subtropical and tropical habitats (subgenus Scleria).
One section, Hypoporum, is recognised in subgenus
Hypoporum, pending survey of the subgenus on a world basis.
Four sections are recognised in subgenus Scleria,
namely, Scleria, Acriulus, Schizolepis and Ophryoscleria.
Section Scleria may comprise several natural groups, the
delimitations of which can not be attempted until a world
survey has been made.
A map showing world distribution of the genus, and
regional distribution maps of Southern African species
are provided, also a Table showing the total distribution
range of species recorded from Southern Africa.
Generic, subgeneric, sectional and species
descriptions are provided. Two new species are described.
Keys to the Southern African species for use in the
herbarium, in the field, and one based on anatomical
characters of the laminas are presented. Original
descriptions and photographs of type specimens of taxa
represented in Southern Africa are included as appendices. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1983.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/11144 |
| Date | January 1983 |
| Creators | Franklin, Esme Frances. |
| Contributors | Gordon-Gray, K. D. |
| Source Sets | South African National ETD Portal |
| Detected Language | English |
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