Flower Biology and Pollinators of the Amazonian Monoecious Palm
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I99O] OLESENAND BALSLEV:MIMICRY r81 Principes,34(4), 1990, pp. I8l-190 Flower Biology and Pollinatorsof the AmazonianMonoecious Palm, Geonomamacrostachys: A Caseof Bakerian Mimicry JnNs Mocor'{sOLESEN AND HENRIK Bersrsv Botanical Institute, Llniuersity of Aarhus, Nordlandsaej 68, DK'824O Risskoa, Denmark Assrnecr f.rme3 km S to Afiangu,Rio Napo,Yasuni National Park, Ecuador (00o32'S, understory Ceonoma The protandrous palm, 76"26'W) at 300 m a.s.l.,April l3-28, macrostachys Mart., has staminate and pistillate phases of at least 4 and 3 days duration, respectively. 1986. The population of Geonoma The staminate flower offers pollen and possibly euglos- macrostachysstudied was delimited in part sine active compounds to visitors, while the pistillate by standsof Heliconia (Heliconiaceae),and probably does not present food rewards. The pistillate partly by relatively large Geonoma-free flower resembles the staminate in size. color. and scent; it has a staminodial tube, and is pollinated by areas.The areaoccupied by the population imitation of the staminate andlor by provision of sites was estimatedto be 2.5 hectares. The for mating and eggJaying. The inflorescence is visited ground vegetationis poor in speciesand by 22 species of insects and arachnids during its consistsmainly of G. macrostachys. lts staminate phase and l0 species during the pistillate density was estimated as 200 individuals phase. Visiting insects include drosophilids, bees, syr- phids, and beetles. Trigonids and drosophilids are per hectare. Only five individuals inside probably the most important pollinators. the study area flowered during the study period. They were all kept under obser- In his review of palm pollination Hen- vation.Fluorescent pigments (RADCLO @, derson (1986) concludesthat the palm HerculesKemiska AB, Box 300, 40I 24 family possessesa great diversity of pol- Giiteborg, Sweden) were used as pollen lination modes. Beetles,bees, and flies are mimics to study pollen flow (Stockhouse the main groups of pollinators. 1976). In the study area 62 infructes- This paper reports on flower biology and cencesof G. macrostachys were found. diversity of inflorescencevisitors of Geon- Of these 50 were collectedand fruit set 'We oma macrostaehysMart., a common estimated. censusedabundance and understory palm in Amazonian Ecuador. visitation of flower visitors. Specimensof It is acaulescentwith undivided leavesand the insect species visiting the inflores- has an erect spicate inflorescence.Like cenceswere preserved in ethanol.Voucher other geonomoid palms it is monoecious specimensof plants are depositedat Her- (Wessels and protandrous Boer 1968, Uhl barium AAU and Herbarium QCA. Insect and DransfieldI987). specimensare depositedat The Natural History Museum, Aarhus, Denmark, and StudyArea and Population The EntomologicalDivision, QCAZ, Pon- This study was conductedin tropical tificia Universidad Cat6lica del Ecuador, lowlandrainforest on the non-floodedterra Quito. PRINCIPES [Vor. 34 l. Inflorescence of Geonoma macrostachys. A-B, inflorescence in staminate phase (arrow in B: small trigonid bee, compare Fig. 5:lI); and C, inflorescence in pistillate phase. FloralBiology about 1400 hours or at least before the next morning when a new pulse of sta- Geonomamacrostachys is monoecious minate flowersopens. If the weather is dry and protandrous. As in other geonomoid at the time of withering, the staminate palms its flowersare groupedin triads con- flowersturn brown and fall off. When rain- sisting of two staminate and one pistillate, ing some of the flowers turn brown and sunken in pits on the spike. Corolla, fall off while the rest remain on the inflo- androecium, and gynoecium are white. rescenceas a wet massof decayingmate- Staminate flowering lasts four days or rial. Immediately after the opening of the more per inflorescence,with daily pulses three petalsthe six inflexed stamensdeflex ofup to 200 flowersper inflorescence(Fig. partly (Fig. 3A-D). A small vestigial gy- lA,B). The newly openedflowers are usu- noecioid structure (pistillode) is found on ally restricted to a part of the spike. For the inner side of the wall of the androecial exampleon April 15, most flowers were tube (Fig. 3G). Pollen grains vary in shape found on the upper third of one of the (Fig. 3E). Their length averages39.6 + inflorescences,on April l6 most were found 2.5 pm (N : 200, from 5 differentflowers, on the middle part, and on April 17 most range 32-46 pm, Fig. 4). Neither the sta- were found on the lower part. All staminate minate nor the pistillate flower seem to flowers in the studied populationopened produceany nectar. within one half hour between 0900 and The pistillate phasestarts the day after 1000 hours (Fig. 2). Withering occurs the last staminateflowering pulse. The pis- r9901 OLESENAND BALSLEV:MIMICRY Time of Day next day 9 10 11 12 13 14 15 18 9 10 Visitor Group ( numbers,compare fig. 5) Curculionidae (1,2) s P Nitidulidae (4,18) S P SmallTrigonidae(ll) s P LwgeTrigonidae s P Euglossa ignita (12) S Halictidne (19) S Drosophilidae (13) S P Syrphidae(20) s Otherflies (9, 21) S P 5 individualsat a time per inflorescence * = main flowering period 5 extended flowering on 25 very rainy days 2. The diurnal pattern of visitation of the different insect groups to inflorescencesof Geonoma macrostachys in relation to flowering. Numbers in parenthesesrefer to illustrations in Fig. 5. S: staminate inflorescencevisitors; P: oistillateinflorescence visitors. tillate phase lasts at least 3 days. The num- and tannin tissue in the androecial and ber of new flowers per inflorescence per staminodial tubes (Fig. 3F,J). day and the tendency to present flowers During the study period staminate and concentrated on restricted parts of the oistillate inflorescences were never found inflorescence are less than during the sta- closer to each other than about 100 m. minate phase (Fig. lC). The pistillate flow- Fluorescent pigments were used many times ers open about one half hour earlier than on staminate flowers, but were never the staminate (Fig. 2), and remain open refound on pistillate ones. Fruit set was, until the next morning, and sometimes old however, high on almost all infructes- and new pistillate flowers are found inter- cences with about 0.55 fruits/pistillate mingled. Within the petals a staminodial flower (N : 50). conspicuous (Fig. 3H). The stigma tube is InsectVisitors is covered by a thick layer of adhesive cells (Fig. 3I). Staminate flowers produce Several groups of insectsvisit the inflo- a strong sweet scent, which is emitted from rescences especially during the morning the bud as early as one hour before anthe- hours (Fig. 2). The inflorescenceis visited sis. The pistillate has a weaker scent. Both much more frequently during its staminate flower types contain abundant idioblasts phasethan during the pistillatephase (Fig. 184 PRINCIPES [Vor. 34 0& 'fu 06 F I {l gl Ju 0luw 3. Flowers of Geonoma rnacrostachys. A: staminate flower (p: petals, s: sepals,a.t.: androecial tube), B: bud, C: immature androecium, D: young stamen, E: pollen grains of varying shape,F: idioblast,G: gynoecioidstructure, H: pistillate flower (s.t.: staminodial tube), I: stigmatic tissue (cross section),J: tannin cells in the parenchymatous tissue of the staminodial tube (stained with FeClr). 2). The number of visitor speciescaught, speciesvisited which phaseis given in Ta- while they were foraging on the staminate ble I. and pistillate inflorescencewas 22 and 10, Visitors Included: Two speciesof wee- respectively(Table l, Fig.5). Which vils (Curculionidae, Phyll,olror): One has r9e0l OLESENAND BALSLEV:MIMICRY 185 Numberof Counts(N=200) 44 46 PollenLength, pm Distributionof Pollen Length in Geonomamacrostachys 4. Size distribution of pollen grains of Geonoma macrostachys. a light brown body with a dark patch in Two ant species (Formicidae): They the middle of each elytron (Fig. 5:I). The patrolled up and down the spike, a small other one has a light brown body with black black one with big eyes (Fig. 5:7), and a elytra and thorax (Fig. 5:2). big brown one with small eyes(Fig. 5:8). At least four different species of leaf Two stinglessbee species (Trigonidae) beetles (Chrysomelidae):They were for- 7 mm and 2.5 mm long: The small one aging on the staminateinflorescence. Two with lieht-colored abdomen and dark tho- belongto Acticinae: a light brown one (Fig. ,u* und head (Fig. lB,5:11). The larger 5:3), and one with light brown body, dark onewas completely black. The smallspecies elytra and very thick hind legs(Fig. 5: l7). was observed collecting pollen and had One speciesis a green tortoise beetle (Cas- white corbicular pollen loads.They walked sidinae)(Fig. 5:15). The fourth species around on the inflorescence. The larger with a black-light brown elytra belongsto bee specieswas observedseveral times' Galerucinae(Fig. 5: l6). flying around the inflorescence,but it was Two Nitidulidaespp. (Fig. 5:4, l8). never seen landing. Two rove-beetles(Staphylinidae): The A green orchid bee species Euglossa larger one is completelyblack (Fig. 5:5), ignita (Apidae): It foraged from the not while the smaller one has a light-colored fully openedstaminate flowers. Only male hind body with a broad dark stripe (Fig. beeswere observed(Fig. 5:12). 5:6). Two individuals of a sreen iridescent 15 \/ ffi\u 'r... ur-"* 0[u* r9901 OLESENAND BALSLEV:MIMICRY 187 Table 1. Visitors to staminate and pistillate phases of the inf.orescenceo;f Geonoma macrostachys. Visitation Visitor Taxon Staminate Pistillate Class Insecta, order Coleoptera: Fam. Curculionidae, tribus Derelomini, Phyllotrox sp. l. (I) X x Fam. Curculionidae, tribus Derelomini, Phyllotrox sp. 2. (2) X x Fam. Chrysomelidae,subfam. Acticinae sp. l. (3) o Fam. Chrysomelidae,subfam. Acticinae sp. 2. (17) o Fam. Chrysomelidae,subfam. Cassidinaesp. (I5) o Fam. Chrysomelidae,subfam. Galerucinae sp. (16) o Fam. Nitidulidae sp. 1. (4) x x Fam. Nitidulidaesp. 2. (18) x x Fam. Staphylinidae sp. I. (5) o Fam. Staphylinidae sp. 2. (6) o Order Hymenoptera: Fam. Formicidaesp. l. (7) o Fam. Formicidae sp. 2.