The palata smell so charac­ teristic of the Lowveld is pro­ Botanical brainteaser duced by the insignificant flowers of the polato bush, Phyllanthus reticulatus. The fruits are small black fleshy berries. Photo C Vogel. Fruits have flipped (Thanks to Stephen Net of Biyamili Camp, Kruger National L Park, for 109 one for m~to from fleshy to dry photograph.) and back? Are fruits adaptable regardless of genetic heritage? by AntonI V. MIlewski, Percy fitzPatrIck Institute of African Ornithology, University of Cape Town Lnnaeus started a tradition of classifYing plants mainly by elaiosome (and thus gathered and buried by ants) to those their flowers. To this day, herbarium specimens are not val­ with large, conspicuous wings reminiscent of Dodonaea or ued for identification, unless they include flowers. The idea Zygophyllum, for example Cliffonia burgersii. Cliffonia is accepted by many botanists and amateur plant enthusi­ conifera and a few other species have cones similar to those asts that the flower reveals the true origins of a plant, even of Leucadendron, which presumably protect the seeds where the vegetative structures (such as stems and leaves) against fire, and then shed them to the ground after fire. But have been greatly modified by adaptation to particular envi­ perhaps the biggest surprise is that one species, C. baccans, ronments. However, modern taxonomy takes a more com­ has bright orange fleshy fruits, suggesting dissemination by prehensive approach in which flowers are acknowledged to small birds in fYnbos vegetation. be subject to adaptation themselves. As a result, it is being Several genera generally lacking fleshy fruits contain increasingly recognized that a single genus can include flow­ coastal species with fleshy fruits. Passerina ericoides of sea­ ers of strikingly different form, attracting quite different pol­ side dunes near Cape Town has bright red fruits, attractive linators. Microloma and Gladiolus are examples. to birds, in sharp contrast to P. corymbosa of inland areas, Could taxonomists profitably apply the same new thinking which has dry fruits, so small and dull that they are over­ to fruits? At the moment, it appears that several genera are looked. Chasmanthe aethiopica of seaside thicket-edges dif­ still distinguished mainly on the basis of their fruits. Is this fers from other Iridaceae (including other members of the valid, or should we accept that fruits are adaptable accord­ same genus) in having capsules that open without dehiscing, ing to ecological circumstances, regardless of the genetic her­ thus displaying the seeds against the red inner surface of the itage of the genus? capsule. Because each seed is dressed in a succulent, The southern African flora contains striking examples of orange-coloured layer, the plant achieves analogy to fleshy the adaptability of fruits. In particular, I have been surprised fruits. The seeds are removed from the capsule cup by birds, continually to find examples of fleshy fruits in various genera such as the Cape bulbul (as witnessed by bulb expert, that otherwise have fruits that are dry or dehiscent (fruits Graham Duncan) that digest the orange succulent layer but that dry out and split open to release seeds). Fleshy fruits are cannot digest the seed. designed to be swallowed whole by frugivorous (fruit-eating) Thesium has many species in fYnbos, in which the seeds birds and other seed-disseminating vertebrates, such as fallout of the open capsule, and are then sown by ants. large mammals. However, several species occurring in the Karoo have fleshy A good South African example is Chironia baccifera, which fruits, attractive to birds. Perhaps the clearest example is T. has bright red fruits, resembling small tomatoes. By con­ trijlorum, in which the fruits are bright red. Most species of trast, its close relative Chironia palustris has small dry fruits Asparagus have fleshy fruits. However, at least one species unattractive to birds. Tetragonia (Aizoaceae) in South Africa (A. exuvialis) has fruits that are dry when ripe, and are not has either winged fruits (e.g. T. decumbens) or burr-like known to be attractive to birds. fruits (e.g. T. echinata). Yet, in Australia, the common T. Euphorbiaceae have adaptable fruits implexicoma has succulent red fruits disseminated by vari­ The Euphorbiaceae contains several examples of variation ous birds. Solanum shows a converse pattern. Botanist David in fruit-form within genera. The potato smell familiar to nat­ Symon of the South Australian Herbarium has shown that uralists in the lowveld is produced by Phyllanthus reticulatus. several species of this cosmopolitan genus (which also con­ The fruits are small, black and fleshy. This belongs to a cos­ tains the domestic potato and eggplant) have dry fruits lack­ mopolitan genus, of which some species have fleshy fruits ing any fruit-pulp. He has found evidence that the seeds are attractive to birds, and others have dry capsules. Euphorbia inanimately dispersed by various means according to the is extremely variable in stem and leaf form, and to a lesser species in dry climates in Australia. degree fruit form. The seeds of many species of Euphorbia are Fynbos plants can produce fleshy fruits expelled when the capsule dries out and spontaneously The genus Cliffonia is extraordinarily variable in fruit form, explodes. Despite the misleadingly red colour and bright as shown by a recent revision by Chris Whitehouse of the gloss of the unripe capsules, the seeds are designed to land University of Cape Town. Fruits range from those with an directly on the ground, once ripe. 118 September 2004 Veld&Flora An odd species out in the genus is fleshy fruits so prized as human food genera with similar flowers but dry Euphorbia damarana. This stem-suc­ that they are cultivated in orchards! No capsules, such as the Australian culent of the edge of the Namib has rel­ South African would expect Terminalia Sarcozona? atively large fruits that turn yellow to have fleshy fruits. Yet, various There are still many unanswered when ripe, and are eaten to this day by species in this genus have fleshy fruits questions about modes of dissemina­ the black (or hook-lipped) rhino. A in south-east Asia and Australia. In tion in the flora of southern Africa, recent television documentary has parts of tropical Australia, the ripe even in common species. It might be depicted the seeds being sown in the fruit-pulp of Terminalia was a staple illuminating to do a study comparing faeces of the rhino in Damaraland. food for aboriginal people. In the case the degree ofvariation in flowers versus Herbivorous mammals such as·rhinos of T. catappa of the Indian Ocean fruits, within genera. This would begin cannot see the full spectrum of colours coasts, the fruit combines an edible to test a new notion that both pollina­ seen by birds and primates. However, it fleshy layer with a corky layer - ensur­ tion and dissemination agents can vary has been established conclusively that ing both flotation and dissemination by widely within genera, according to eco­ the horse can see yellow, which sug­ animals. logical rather than genetic reasons. gests that its relatives the rhinos can Valid genera? Perhaps this is a project that would be see the same hue. I wonder whether several genera cur­ suited to the interested amateur? For The forest tree Elaeophorbia rently distinguished on the basis of example, Phylica appears to show con­ drupifera has yellow fleshy fruits, but is fruit form are valid? For example, servatism in its fruits. otherwise extremely similar to Chrysanthemoides is a spectacular Euphorbia teke, found in the same example of the ability of plants to areas. Recent molecular studies have evolve fleshy fruits afresh. This genus indicated that the genus Elaeophorbia ­ has typical daisy flowers, yet is unique I wonder whether several despite its fleshy fruits - belongs deep among Asteraceae in its succulent, genera currently distin­ within the genus Euphorbia, which sweet fruits, which must have been one generally has dehiscent capsules. of the most rewarding foods for the guished on the basis of Another member of the Euphorbiaceae, hunter-gatherer. Osteospermum has fruit form are valid? Croton sylvaticus, has conspicuous, the same common name (bietou), soft, orange-coloured fruits, and its because its flowers are similar and its seeds are disseminated by the green leaves are likewise palatable to domes­ pigeon, a thoroughly frugivorous bird. tic and wild hoofed animals. However, The Rhamnaceae include several This contrasts with other members of it has different fruits, such as the bird-disseminated genera with fleshy the genus Croton, which have dry fruits winged (wind-dispersed) fruits of 0. sin­ fruits, such as Rhamnus itself. The ignored by frugivorous birds, and uatum. If these genera have been sepa­ developing fruits of most species of destroyed by seed-eating squirrels rated in the past mainly because of Phylica give a false promise, with a red­ Savanna plants and large animals their fruits, perhaps Chrysanthemoides dish blush on the green capsule, Acacia shows a wide variation in fruit and Osteospermum would be more cor­ resembling an appetizing apple in form in southern Africa, even within rectly regarded as one genus. A similar miniature. The nearly-ripe fruit of P. the same environment. For example, argument put forward by Felix Forrest buxifolia is so conspicuously red that Acacia mellifera and A. erioloba can be is worth examining in the case of this species has been widely described found side-by-side over large areas in Nylandtia (large red fruits, disseminat­ as having a fleshy fruit. However, all the Northern Cape. Of these two ed by tortoise and humans) and species of Phylica that I have so far species, swarthaak has papery pods, Muraltia (disseminated by ants), which investigated fail to produce ripe fruit­ ensuring dispersal of the seeds by are related genera of Polygalaceae.