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The genetic fingerprinting of criminals
no longer belongs to the realm of sci-
ence fiction. Similar molecular data has
become a common tool at the disposal of
plant taxonomists, contributing tremendously
to the better understanding of how plant fami-
lies are related to each other. However, when
descending from the rank of family down the
hierarchy of life, ranks below, i.e. groups of
genera, individual genera or species, have not
all yet been reliably identified by molecular
means. This holds especially true for the vygie
family (Aizoaceae/Mesembryanthemaceae)
where researchers have failed to get meaning-
ful groupings of genera or species after analys-
ing a number of genes.
Yet, species remain the most fundamental
rank in our line of work. Clear and reliable
species boundaries are required not only for
taxonomic purposes, but also for conservation
endeavours. Delosperma herbeum and D. davyi
are a case in point. D. davyi is known from a
few populations in Gauteng and is listed as a
Red Data species. Its conservation is thus cur-rently actively mediated by nature conserva-
tion authorities. However, D. davyicould be a
mere variety or ecotype of the widespread D.
herbeum, in which case it is not in need of con-
servation. Differences between the two species
lie in growth form, with D. davyi developing
long, trailing or climbing, persisting vegetative
branches as opposed to the predominantly
erect annual flowering branches in D. herbeum.
From an ecological perspective, D. davyioccurs
in shady riverine woods and D. herbeum occurs
in open grassland.
In the view of the highlighted inability of
gene sequencing to provide meaningful data,
a different molecular technique known as
amplified fragment length polymorphism
(AFLP) was considered. Instead of determin-
ing the order of all the building blocks in a
particular gene, as is done in gene sequencing,
the entire DNA content of the plant is chopped
up into fragments beginning and ending with
predetermined short sequences. Plants that
share the same complement of fragments are
perceived to be related. The AFLP technique
has been used with great success in studying
taxonomic issues below the rank of species, i.e.
at the population level, and is therefore ideally
suited to address the D. davyi/D. herbeum issue
mentioned above. But, could this techniqueperchance also distinguish between vygie spe-
cies, keeping in mind that many fynbos fami-
lies and genera (vygies included) appear to be
recently evolved, and perhaps, from a molecu-
lar point of view, still act like populations?
In response to the D. davyi/D. herbeum affair,
a number ofDelosperma herbeum populations
from the North West, Gauteng, Free State and
Limpopo provinces of South Africa were ana-
lysed as well as a single population ofD. davyi
(see accompanying map). To test the AFLP
technique to distinguish between vygie spe-
cies, populations of D. knox-daviesii, D. gau-
tengense, D. purpureum, D. leendertziae and
D. vogtsii (all occurring in Gauteng) were also
included in the study.
After scoring a total of 158 fragments for 99
individuals representing a total of 30 popula-
tions, a cluster analysis, where individuals are
grouped/clustered on the basis of shared simi-
larities, was embarked upon. The majority of
individuals formed locality-specific groupings.
In addition, some broad correlations appear to
exist between the clusters obtained in D. her-
beum and their distribution. The Sun City and
Groot Marico populations (labelled 21 and 22
on the map) form a cluster to the north-west of
the study area. There also appears to be a con-
nection between the north-eastern Pretoriaand Naboomspruit populations (labelled 19
and 20 on the map). The geographic signal in
the Vredefort Dome (populations 5-7) is less
clear. Population 5 clusters with samples from
Potchefstroom and Klerksdorp, whereas popu-
Delosperma gautengense with broader petals than found in D. herbeum. Photo: M.H. Buys.
modern techniques in plant taxonomy
Discovering the Delosperma family tree via molecules
Mesembs and Molecules
by M.H. Buys, Compton Herbarium, South African National Biodiversity Institute, Kirstenbosch and Dept.
of Botany and Zoology, University of Stellenbosch
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lation 6 has ties to the north, clustering with
the population from Fochville, and population
7, from south of the Vaal River, has apparent
similarities with the populations to the north-
east ranging from Sasolburg to Johannesburg.
D. davyi and D. herbeum from North Riding
form a cluster separate from the remaining
populations ofD. herbeum.
While the above results are somewhat
ambiguous regarding the status of D. davyi,
further statistical analyses not reported here,
as well as morphological considerations, sug-
gest D. davyito be a superfluous name.
The AFLP data can readily distinguish
between species of Delosperma. The yellow
flowered D. vogtsiigroups with the white flow-
ered D. gautengense. The mauve coloured D.
knox-daviesii attaches itself, in turn, to this
group. The yellow flowered D. leendertziae
groups with the mauve flowered D. purpureum.
The yet unidentified and possibly new mauve
flowered species from Ditholo clusters with themainly white flowered D. herbeum.
Although flower colour is known to be an
unreliable taxonomic character, it was tempt-
ing to consider species with similarly col-
oured flowers and of equal morphology, e.g.
D. leendertziae and D. vogtsii, to be one and
the same entity. Our results suggest this not
to be the case. Where-as DNA sequencing
approaches have failed to resolve even generic
relationships - let alone species - in the vygie
family, the AFLP technique holds promise for
vygie systematics at lower ranks.
*Extracted and modified in part from Buys et al. 2008.
Applying AFLPs in Aizoaceae: The Delosperma herbeum
complex as a case study. Biochemical Systematics and
Ecology36, 92-100, with permission from Elsevier.
TOP: Delosperma davyiwith the typical longer leaves and internodes which are prob-
ably due to the shady habitat in which it occurs.
ABOVE : Delosperma herbeum, the most widespread Delosperma species in Gauteng
and North West provinces. Flowers here pure white.
ABOVE RIGHT: Delosperma vogtsii, resembling D. leendertziae, but on average possess-
ing more petals than the latter and distinguishable based on AFLP data.
BELOW: Delosperma leendertziae, resembling D. vogtsii, but on average possessingfewer petals than the latter, and distinguishable based on AFLP data.
BELOW RIGHT: Transfer of knowledge. Heidi Hartmann pointing out diagnostic charac-
ters ofDelosperma herbeum to Wim Buys.
LEFT: Delosperma knox-daviesiiwith petals more numerous than in D. purpureum.
BOTTOM LEFT: Delosperma purpureum with broad petals similar to D. gautengense. Note
mauve filaments. Photos: M.H. Buys.
