KAROO VIOLETS AND POLLEN WASPS
by Sarah Gess, Albany Museum, Grahamstown
he name Karoo violets is most short filaments. In Aptosimum the Namaqualand and C. gariepensis commonly applied to species shorter pair of stamens is sterile. from the northern Richtersveld T of Aptosimum and the closely The anthers are adpressed in pairs northwards through Namibia). related genus Peliostomum. They and positioned dorsally in the These little wasps, on average about produce an abundance of violet flower. The style is situated in the 10 mm long, are sturdily built and coloured flowers and are a striking dorsal groove. In the freshly opened have markedly club shaped feature of the Karoo. However, it is flower the stigma barely projects at antennae and long retractable only in colour that the flowers are the mouth of the corolla but with tongues. They are blackish and have similar to those of violets. time the style elongates and curves red or red and white markings. They They are not members of the downwards. visit flowers to collect nectar for Violaceae family but of the their own nourishment and Scrophulariaceae, which to mix with pollen for includes such familiar provisioning their nest garden flowers as penstemon cells which are constructed and snapdragon. from soil moistened with The name Aptosimum is nectar and, depending on Greek in derivation, a species, are sited on plant meaning not and ptosimos stems, in groups on stones meaning deciduous (which or in cavities in the in turn comes from ptosis ground. meaning 'fall') and refers to Celonites are ideal polli the fruit, a capsule which is nators as they fit snugly retained on the plant even into the flowers and when after the seeds have been drinking nectar are obliged released. Probably the most to penetrate deeply into the familiar Karoo violet is the flower as the extended widespread Aptosimum tongue matches the length procumbens, also known as of the narrow tube at the Karoo carpet-flower. This base of which the nectaries common name like its are situated. In this specific name alludes to the position the hind end of growth form of the plant, a the wasps' thorax is dense prostrate mat that can immediately beneath the grow to 500 cm across. Not anthers which, when ripe, all species are prostrate deposit a load of pollen Aptosimum spinescens is a onto the back of the wasp. compact spiny shrublet and In fact it seems likely that Peliostomum leucorrhizum a in common with some lax shrublet with remarkably other gullet flowers the white stems. In total there dehiscence of the anthers are about forty species of - , is probably triggered by the Aptosimum and A Karoo violet, or Karoo carpet-flower, Aptosimum indivisum insect visitor. A wasp Peliostomum. All are on the roadside near Prince Albert. Photo: Dave McDonald. emerging from a flower African and most (about after having been liberally thirty) are concentrated in the In the course of our study of showered with pollen visibly bears south-western semi-arid regions. wasps and bees in the semi-arid a blue-grey dusting. Such a wasp, The flowers are clearly designed areas of southern Africa Fred Gess when entering a flower in which the to attract insects and their shape and I have observed the visitors to stigma has elongated so that the and colour led to the assumption many species of these plants in the receptive stigma is pointing that bees ar~their pollinators. They eastern, southern, western and downwards, inevitably wipes off are 'gullet flowers', which means northern Karoo, and in Namaqua some of this pollen and in so doing that the corolla is tubular over the land, Namibia and the southern pollinates the flower. greater part of its length, and very Kalahari. They were receiving only In the Richtersveld National Park, narrow in the basal region protecting occasional visits from bees but in addition to two Celonites species, the nectaries from all but long everywhere were visited by pollen we found another similarly sized tongued or minute visitors. The wasps (Vespidae: Masarinae), partic pollen wasp, recently named and greater part of the corolla tube is ularly from the genus Celonites. described by Fred as Masarina wide but the lower surface is invagi Although there were other plants in peliostomi, which, as its name nated requiring all but the smallest flower, none of these were visited suggests, is closely associated with visitors to push their way into the by Celonites of the species visiting Peliostomum. flower. There are four stamens in the Karoo violets (c. clypeatus and Also visiting Karoo violets are two pairs, a pair with relatively long C. andrei throughout the Karoo, much smaller pollen wasps filaments and a pair with relatively C. peliostomi particularly in species of Quartinia. These minute
170 Veld &' Flora December 2000 wasps, only about 5 mm in length, Acknowledgements are generally too small to pollinate Thanks are due to my co-worker Fred Gess, Harvard University Press for permission to the flowers as they can come and go reproduce illustrations from my book The without transferring pollen. Pollen Wasps (excepting those depicting However, under very dry conditions Celonites gariepensis and Masarina the flowers of such species as peJiostomi), Robin Cross of the Electron Microscopy Unit, Rhodes University for Peliostomum leucorrrhizum are taking the scanning electron micrograph often too small for Celonites to and the Foundation for Research enter. Under such conditions all is Development for a running expenses grant. not lost as the Quartinia species then take over as pollinators. About the author Sarah has an M.Sc. in botany and a Ph.D. Of the occasional bee visitors, the in entomology and finds these two disci most noticeable to a casual observer, plines inseparable. She and her co-worker, are the large grey and white banded Fred Gess, have spent the past 30-odd anthophorine bees, Amegilla years studying solitary wasps and bees in the semi-arid areas of southern Africa as niveata, generalists which are well as in Arizona and Australia. Sarah's attracted to the flowers but are too particular fields of interest have been large to enter. Other bees at the nesting and flower associations. Her book, northern Karoo/savannah fringe are The Pollen Wasps: Ecology and Natural ]-[istOIy of the Masarinae (1996, Harvard small andrenid bees, Meliturgula University Press, Cambridge, Mass) is haematospila. These are probably available for sale through the Botanical too small to be effective pollinators Society Bookshop at Kirstenbosch. and anyway are not reliable visitors Scanning electron micrograph of the like the specialist Celonites species A list of scientific references is available on request from the Publications Manager posterior end of the thorax and anterior as they are generalists visiting a at the Botanical Society, Private Bag X10, end of the abdomen of Celonites relatively wide range of flowers. Claremont, 7735. Tel (021) 797 2090, fax peliostomi showing deposition of pollen. For those wishing to observe for (021) 797 2376, e-mail
Above. Celonites gariepensis, with a grey dusting of pollen, flying to a flower of PeJiostomum in the Richtersveld National Park. Left. Masarina peliostomi entering a flower of Peliostomum in the Richtersveld National Park. Photos: Robert Gess. Right. The perfect fit: Aptosimum procumbens, half flower cut longitudinally, and Celonites clypeatus profile with legs and IOmm wings omitted.
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