Pollination Biology and Taxonomy of Dinemandra and Dinemagonum (Malpighiaceae)
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Systematic Botany (1989), 14(3): pp. 408-426 ?) Copyright 1989 by the American Society of Plant Taxonomists Pollination Biology and Taxonomy of Dinemandra and Dinemagonum (Malpighiaceae) BERYL B. SIMPSON Department of Botany, The University of Texas at Austin, Austin, Texas 78713 ABSTRACT. Dinemandra and Dinemagonum, the only two genera of Malpighiaceae in Chile, have calyx glands borne on stalks rather than appressed to the surfaces of the calyx lobes as is typical of malpighs. It is proposed that this positioning of the glandular secretory surfaces (elaiophores) on the ends of stalks provides an intergland distance and surface area needed for the robust Centris bees that serve as pollinators. The structure of the stalked calyx glands and similarities in pollen provide evidence for the close relationships of the two genera despite their traditional placement in different tribes. However, the sister group of the two genera is impossible to determine at the present time. Extensive collections of both genera in the desertic regions of northern Chile where they are endemic has shown that each is monotypic. The previous recognition of several species in each genus resulted from few available specimens and a tendency, particularly in the case of Dinemandra, for plants from small isolated populations to have rather distinctive morphologies. Of all of the countries in South America, Chile bination with pollen and nectar as part of the has the fewest taxa of Malpighiaceae, two gen- larval provisions. Only four genera of the Mal era, DinemandraAdr. Juss. and DinemagonumAdr. pighiaceae are known to have stalked glands: Juss., each with only one species. This low di- Dinemagonum, Dinemandra, Heladena Adr. Juss., versity undoubtedly stems in part from the fact and Henleophytum Karsten. Dinemandra and Di- that Chile lacks moist tropical and subtropical nemagonumare distinctive in having gland stalks habitats, in which most malpighs are found. 1.4-2.5 mm long. In addition, the stalked glands Moreover, the subtropical portion of Chile is are basally connate, forming pairs between xeric and separated from similar areas of Ar- glands on adjacent sepals. As might be expected, gentina (which could serve as sources of im- this strange positioning of the glands plays a migration) by the Andes. The Malpighiaceae role in the pollination biology. are generally poorly represented in xeric re- Dinemandra and Dinemagonum also share the gions such as those in northern Mexico, the unique features of 8-colporate, reticulate pollen southwestern United States, and northwestern (Lowrie 1982). Nevertheless, Niedenzu (1928) Argentina. Nevertheless, what the malpighs of placed the two genera in different tribes of his Chile lack in terms of diversity, they make up Pyramidotorae (=Gaudichaudioideae) because in novelty. Morphologically, the two genera are of their distinct fruit morphologies. Both have unusual within the family in their mutual pos- dry fruits that split into three winged segments, session of stalked calyx glands. Most of the but the morphologies of the mericarps differ. members of the Malpighiaceae have two oval Dinemandra has mericarps each of which has glands appressed to the dorsal side of all (five), two large lateral wings on the dorsal surface. or most of, the calyx lobes. These glands, known Dinemagonum has mericarps each with a single as elaiophores, secrete oils that are collected large median dorsal wing. These differences primarily (as judged by documented visits to prompted Niedenzu (1928) to place Dinemandra malpigh flowers) by female bees of the genus in the Hiraeeae (=Hiptageae) subtribe Mascag- Centris (Anthophoridae). For many malpighs, niinae and Dinemagonum in the Banisterieae oils are the only floral rewards produced, and subtribe Banisteriinae. Despite their unusual Centris species are therefore the primary or ex- morphology, few botanists have discussed the clusive pollinators. Centris presumably uses the relationships or biology of the two genera. oils collected from these glands similarly to those Works on the vegetation of northern Chile, such collected from other oil-secreting species (Neff as those of Reiche (1907) and Johnston (1929), and Simpson 1981; Vogel 1974), to mix with soil merely commented on their presence. to form part of the nest lining and/or in com- In this article I examine the unusual morx 408 1989] SIMPSON: DINEMANDRA & DINEMAGONUM 409 phology of the flowers of Dinemandra and Di- was acetolyzed according to the methods of nemagonum,relate the floral morphology to the Erdtman (1960). Some of the acetolyzed grains pollination system, assess the relationships of were mounted in glycerin jelly for measure- the genera to one another, and provide a sys- ments and the rest were floated onto SEM stubs. tematic revision of both genera. The problems Some grains were cut open by cutting across a involved in trying to find their nearest relatives stub with the edge of a microscope slide before are also discussed. coating. Stubs were coated with gold and viewed as above. MATERIALSAND METHODS Anatomy. Fluid-preserved buds, open flowers, and initiating fruits were dehydrated, Pollination Ecology and Insect Behav- embedded in paraffin, sectioned transversely at ior. Throughout the month of October 1983, 30 ,um,and stained with safranin and fast green. field observations and photographs of floral vis- Petals of Dinemagonumwere rinsed, stained with itors were made across the ranges of both gen- osmium, and sectioned. Petals of Dinemagonum era. Because Dinemandraand Dinemagonumgrow were also cleared and photographed in water. in the Atacama Desert region of northern Chile, where rainfall is sparse and erratic, it is often RESULTS difficult to find populations in flower, and col- lections in herbaria are correspondingly rare. I Pollination Ecology and Insect Behavior was fortunate that in the fall of 1983, the after- (observations and data on pollination were pro- effects of the 1982-1983 El Nifio were being felt vided by John Neff). Three species of antho- and flowering throughout the region was ex- phorid bees, Centris chilensis, C. rhodophthalma, cellent. and C. bucholzi, have been recorded visiting Di- Flowers were fixed in FAA, later changed to nemandraand Dinemagonum(fig. 1). Judging from 70% ethanol, for morphological and anatomical its distribution and the morphology of its oil- studies. Glands were plucked from other flow- collecting setae, Centris escomeli is also likely to ers, placed in chloroform in glass pharmaceuti- be associated with Dinemandra.The other Centris cal vials, and sealed with a blowtorch for sub- of northern Chile are either non-oil-collecting, sequent chemical analysis. Flowers were later or are specialized for harvesting oils of Calceo- removed from solution and the distance of the laria L. (or similar) flowers. The Centris females span across the posterior four glands and the involved are robust, medium-sized bees (11.5- maximum distance between glands across a 14.5 mm long). Females of C. rodophthalmaand flower were measured. Measurements were also C. bucholzi have setal-collecting structures typ- made on sympatrically collected flowers of Kra- ical of malpigh-visiting Centris, putatively the meria cistoidea Hook. and Arn. (Krameriaceae). primitive arrangement for the genus (Neff and The spans across the posterior four glands of Simpson 1981). Females collect oils from the Dinemagonumand Dinemandrawere compared to elaiophores of both mature buds and open flow- each other and to the distance between the out- ers of Dinemagonum,but apparently only from er gland surfaces of Krameriausing a GLM (Gen- open flowers of Dinemandra. No active pollen eral Linear Model) model of SAS (SAS 1982). collection by female Centris was observed, but Floral and Fruit Morphology. Gland ar- a small, pollen-collecting, undescribed, poly- rangements and gross morphology were viewed lectic panurgine bee was abundant on Dine- using scanning electron microscopy. The petals magonumflowers at several localities. Male Cen- and sexual organs were removed from fluid- trispatrol plants of Dinemandraand Dinemagonum, preserved flowers leaving the receptacle, se- but because the flowers lack nectar, they do not pals, and calyx glands intact. This material was visit them. dehydrated, critical-point dried, mounted on The behavior of Centris on Dinemandra and SEM stubs, coated with gold, and viewed with Dinemagonum is basically similar to that ob- a Phillips 313 Scanning Electron Microscope. served on most tropical malpighs. Female bees Anther morphology, stigma positions, and fruits arrive, orient with their bodies along the axis were also assessed using SEM. Individual sta- of symmetry with the head at the flag (often mens, ovaries with intact styles, and schizocarps referred to as the posterior) petal (figs. 2, 3). The were similarly prepared. Pollen of mature buds bees grasp the flag with the mandibles and stroke 410 SYSTEMATICBOTANY [Volume 14 15O 200 250 30? 350 40? I I |Dinemandrc ericoides Dinemagonum goyanum - >- --? oKrcmeriGcistoideG I I _ Centris bucho/zi (13.5 14.5mm) _: | 4 _Centris rhodo,phthc/mG (12.0-13.5mm) W ? ~~~~~~~Centris chilensis (11.5 - 12.5 mm) I I Centris escomeli _ X IZ s (13.5-14mm) FIG. 1. Latitudinal distributions (in degrees south of the equator) of Dinemandra ericoides. Dinemagonum gayanum, Krameriacistoidea, and the Centris species that serve as their pollinators. Centris escomeli has never been collected on Dinemandraor Dinemagonum,but on the basis of its morphology is expected to be a