The species name Craterostigma nanum gets reinstated
by Kate Grieve, Pieter Bester and Graham Grieve
Photographs by G Grieve unless indicated otherwise
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| A close-up view of Craterostigma nanum showing the elbowed stamens and prominent yellow bosses in front. |
The genus Craterostigma is a member of the family
Linderniaceae. There are about 15—27 species of Craterostigma worldwide
(depending on the source), found mainly in tropical and southern Africa, extending
to Madagascar, Arabia and India (Ghazanfar, Hepper & Philcox, 2008; Plants
of the World Online, 2023). They are perennial dwarf herbs and are examples of desiccation
tolerant or resurrection plants.
On Thursday walks at the Umtamvuna Nature Reserve with Tony
Abbott and his group from 2009 to 2019, we were often captivated by colonies of
small plants growing in shallow soil on rock sheets. Among the sedges and mosses
was a Craterostigma, one of the plants that die back and disappear
completely in dry conditions and re-appear during wet periods. However, because
this particular Craterostigma species was not yet identified, it was referred
to as Craterostigma sp. nov. So it remained for several years, until we
decided that this beautiful little plant deserved its own name and undertook to
do something about it.
At that stage there were only two accepted Craterostigma species in South Africa (Fischer, 1992) namely C. plantagineum Hochst. and C. wilmsii Engl. ex Diels.
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| Craterostigma plantagineum from Mogalakwena which lies about 50 kilometers southwest of Polokwane, Limpopo Province (Photos with acknowledgement to Reuben Heydenrich, iNaturalist observation #101884921) |
Craterostigma plantagineum occurs at high altitudes across India and Africa, as far south as the northern provinces of South Africa. It is often found in disturbed areas, grazed or trampled by animals, and along pathways. Although C. plantagineum is also a small plant, it has conspicuous raised veins on the underside of the leaf and the flowers are blueish purple with white edges.
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| Craterostigma wilmsii from the Buffulskloof Privaate Nature Reserve in Mpumalanga province, South Africa. |
Craterostigma wilmsii occurs in the northern provinces of South Africa (North West, Free State, Gauteng, and Limpopo), usually in damp places. It is a taller plant and the flowers are generally pink or mauve.
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| A view of a typical shallow bed of soil on Msikaba sandstone rock in the Umtamvuna Nature Reserve with a colony of Craterostigma nanum accompanied by Delosperma vinaceum and Selaginella dregei. |
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| A small group of Craterostigma nanum in their dessicated, dormant state after a period of dry weather, from the Umtamvuna Nature Reserve. |
Neither of these species matches the Umtamvuna plants. In the course of our
field trips, we discovered that the local Craterostigma occurred only on
Msikaba Formation sandstone rock sheets in
the Pondoland Centre of Floristic Endemism (Van Wyk & Smith 2001), the area
where the type specimen for the species was collected. This region lies along the east coast, falling within the Pondoland-Ugu
Sandstone Coastal Sourveld (Mucina & Rutherford 2006), extending from the
Mzimkulu River at Port Shepstone in the north to the Egossa Fault in Pondoland
in the south and including sandstone outcrops at Uvongo and Port St Johns.
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| A small cluster of white flowered Craterostigma nanum from the Umtamvuna Nature Reserve. |
The
next step was to delve deeper into the literature and examine herbarium
specimens. During this process we discovered a previously described species, C.
nanum, that appeared to be a close fit with the Umtamvuna plants. What had
happened to it?
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| A cluster of pink flowered Craterostigma nanum from Oribi Flats. |
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| A specimen of Crateostigma nanum from the Mkambati Nature Reserve in Pondoland, Eastern Cape. |
In
an early account of the genus by Hiern (1904) in Flora Capensis, three species were listed for the southern African region:
C. plantagineum, C. nanum, and C. wilmsii.
The type specimen for C. nanum was collected by Drège in 1843 between
the Mzimvubu and Msikaba rivers in Pondoland (“Zwischen Omsamwubo und
Omsamcaba”). On a visit to the Compton Herbarium in Cape Town, we could find no
vouchers for C. nanum until John Manning showed us the old collection in
the Flora Capensis section. There at last we were rewarded by seeing Drège’s
specimens, suggesting that C. nanum and our plants could be the same entity. In
Fischer’s (1992) revision of the genus, C. nanum was sunk into C.
plantagineum (for reasons that are not evident) but it was clear to us that
conspicuous differences between the two species warranted re-instatement of the
name C. nanum.
We approached Pieter Bester, principal taxonomist at SANBI in Pretoria, who kindly agreed to help us prepare a manuscript to re-instate the name Craterostigma nanum. The first step involved taking measurements of plants and members of the Pondoland CREW group (formerly the Thursday group) assisted with the fieldwork. We used these measurements and observations of the plants in different localities to compile an updated description of the species. Together with a drawing made from live material, photographs, a distribution map and the background taxonomic literature, a manuscript was prepared and recently published in the scientific journal Phytotaxa - ‘our’ Craterostigma is once again no longer nameless! Currently in iNaturalist, observations of this species are labelled C. plantagineum. With the publication of this re-instatement, hopefully these records can be corrected.
For citizen scientists, this experience demonstrates the contribution to our flora that can be made with the support of CREW and guidance from professional botanists.
References
Ghazanfar, S.A., Hepper, F.N. & Philcos, D. (2008) Craterostigma.
In Flora of Tropical East Africa, p 1.
Fischer, E. (1992) Systematik der afrikanischen
Lindernieae (Scrophulariaceae). Tropische und subtropische Planzenwelt 81:
1–365.
Grieve, K.W. & Bester, S.P. (2023) Re-instatement
of Craterostigma nanum (Linderniaceae) from the Pondoland Centre of Floristic
Endemism and key to the South African species. Phytotaxa 592 (2): 135-143.
Hiern, W.P. (1904) Scrophulariaceae. In: Thiselton-Dyer,
W.T. (ed.) Flora capensis 4 (2). Lovell Reeve & Co., London, pp.
121–420.
Mucina, L., Rutherford, M.C. & Powrie, L.W. (2006) Vegetation
Atlas of South Africa, Lesotho and Swaziland. In L.M. Muchina & M.C.
Rutherford (Eds.) The vegetation of South Africa, Lesotho and Swaziland. Strelitzia
19. South African National Biodiversity Institute, Pretoria, pp.749–790.
POWO (2023). Plants of the World Online. Facilitated
by the Royal Botanic Gardens, Kew. Published on the Internet;
ttp://www.plantsoftheworldonline.org/ Retrieved 27 August 2023.
Van Wyk, A. E. & Smith, G. F. (2001) Regions of
floristic endemism in Southern Africa: A review with emphasis on succulents.
Umdaus Press, Pretoria.
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