BlOTROPlCA 33(4): 596-605 2001 Phenology, Sexual Expression, and Reproductive Success of the Rare Neotropical Palm Geonoma epetiolata’ Silvana Marten2 Escuela de Biologia, Universidad de Costa Rica, San Jose, Costa Rica and Mauricio Quesada3 Departamentode Ecologia de 10s Recursos Naturales, lnstituto de Ecologia, Universidad Aut6noma de Mexico, Apartado Postal 27-3 (Xangari), Morelia, Michoacan 58089, Mexico ABSTRACT We studied the phenology and reproductive biology of the stained glass palm Geonoma epetiolata in a premontane rain forest of Costa Rica. This understory species is endemic to Costa Rica and Panama. We followed 102 plants for two years and found that G. epetiolata is monoecious and protandrous. Flowering duration at the inflorescence level is three to six months for the male phase and two to three weeks for the female phase; this is one the most extended flowering periods reported for palms. Flowering in this palm is continuous throughout the year, both at the individual and population level. This long and continuous flowering pattern may represent an adaptation to increase the chances of reproduction in a environment of high and unpredictable rainfall. The species is self-compatible, hut self-pollination is possible only when there is overlap of male and female inflorescences (38% of the cases). Only 28 percent of the stigmas of 1020 flowers received pollen grains and 20 percent developed pollen tubes in the styles. Of all the flowers produced by an inflorescence, I4 percent initiated fruit development but only 3 percent develop into mature fruits. Seventy-six percent of the initiated fruits were aborted. RESUMEN Estudiamos la fenologia y la biologia reproductiva de la palma Geonoma epetiolata en un bosque hlimedo del pre- montano en Costa Rica. Esta palma de sotobosque es endtmica de Costa Rica y Panami. Durante dos arios observamos 102 plantas marcadas y encontramos que G. epetiolata es monoica y protindrica. La duraci6n de floraci6n a nivel de inflorescencia es de tres a seis meses para la fase masculina y de dos a tres semanas para la fase femenina, este es el periodo de floraci6n mis prolongado que se ha reportado para cualquier especie de palma. La floracibn de esta palma es continua a travts del afio, tanto a nivel individual como poblacional. Esre patr6n de floraci6n largo y continuo parece representar una adaptacibn para aumentar las posibilidades de reproducci6n en un ambiente de precipitacion aka e impredecible. La especie es auto-compatible pero la autopolinizaci6n solo es posible cuando existe traslape de flores femeninas y masculinas dentro de un mismo individuo (38% de 10s casos). Unicamente el 28 por cienro de 10s esrigmas de 1020 Bores analizadas recibieron granos de polen y 20 por ciento desarrollaron tubos polinicos en 10s estilos. De codas las flores producidas por una inflorescencia, en promedio 14 por ciento inician el desarrollo de frutos pero solo el 3 por ciento de las flores llega a producir frutos maduros. El 76 por ciento de 10s frutos iniciados se abortan. Kq, word: bet-hedging dichogamy; fiuit abortion; Geonoma epetiolata; monoecy; palm phenology; polLen limitation. PALMS ARE ONE OF THE MOST ABUNDANT AND DIVERSE mans as materials for construction, ornamental groups of plants in Neotropical rain forests and plants, and food products (Balick 1984, Rich represent important food resources for many spe- 1987, Bernal 1992, Lescure etal. 1992, May 1992, cies of animals (De Steven et al. 1987, Foster 1990, Pedersen & Balslev 1992, Joyal 1994, Durin Foster & Hubbell 1990, Hammel 1990, Prance 1995). Despite the ecological and economic im- 1990, Kahn & de Granville 1992, Clark et a/. portance of palms, the population biology of most 1995, Scariot 1999). Palms are also used by hu- species is still unknown (Scariot et al. 1995). The least studied palms are the habitat special- ists and the species with restricted geographic rang- ’ Received 15 August 2000; revision accepted 30 April es. These species are the most vulnerable to extinc- 2001. E-mail: [email protected]. tion due to the rapid deforestation obliterating Corresponding author. E-mail: mquesada@ibiologia. Neotropical rain forests (Bawa & Ashton 1991, unammx Duran 1995, Whitmore 1997). Therefore, to pre- 596 Reproductive Biology of Palms 597 serve and manage these rare species of palms, it is leaves are reddish and have conspicuous purple essential to understand the factors that influence spots. This feature makes this palm potentially the reproduction and viability of their populations valuable as an ornamental. Seeds have been har- (Bawa & Krugman 1991, Ratsirarson & Silander vested on a small scale to develop commercial nurs- 1996). eries. Aspects related to the timing, frequency, and Geonoma epetiolata is monoecious and protan- synchrony of flowering are directly related to the drous with interfoliar, spicate inflorescences (50 crn breeding success of plant populations (Rathcke & in length) that produce staminate and pistillate Lacey 1985, Clark & Clark 1987, Marquis 1988). flowers in separate sexual phases. Pistillate flowers Flowering synchrony and intensity have been are dark red and they have a tubular corolla that shown to affect visitation by pollinators, which in measures 4-6 mm in length. Staminate flowers turn determines fruit set (Augspurger 1981, 1983). have a 2 mm corolla and 6 protruding stamens, These aspects of flowering phenology are particu- which have red filaments that are 5-6 mm long, larly important in monoecious plants because tem- and white anthers. Both flower types lack nectar poral differentiation in the expression of unisexual (Marten 1998). Mature fruits are purplish black flowers determines the mating patterns within and and single-seeded. among populations (Bullock 1981). Many Neotropical palms are monoecious, but STUDYsire.-The study was conducted at Rara little is known about the relationship between sex- Avis Private Reserve in Sarapiqui, province of He- ual expression patterns and the reproductive success redia, Costa Rica (10"15'N, 84"05'W) . This re- of rare palms (Henderson 1986, Ratsirarson & Sil- serve is located at 560 to 800 m in elevation and ander 1996). In this study, we examined the rela- borders the Braulio Carrillo National Park. Mean tionships among phenology, sexual expression, and annual rainfall is between 7000 and 8000 mm and reproductive success in Geonoma epetiolata H. E. there is no regular seasonality. The vegetation is Moore, a monoecious palm, found only in a few premontane rain forest (Holdridge 1967). localities of Costa Rica and Panama. To our knowl- edge, this is the first study on the reproductive bi- INFLORESCENCEDEVELOPMENT.-we determined the ology of this rare palm species. The main objectives development of 100 inflorescences on 78 individ- of our study were to: (1) characterize the repro- uals from December 1995 to October 1997. For ductive phenology of G. epetiolata at the inflores- each inflorescence we recorded the longevity of the cence, individual and population level; (2) evaluate following phases: (a) elongation phase: time elapsed the spatial and temporal variation in gender ex- between the emergence of the inflorescence from pression; (3) determine the relationship between the bract to the beginning of flowering; (b, c) sta- pollination success and reproductive output with minate and pistillate phases: times of male and fe- flowering phenology; and (4) ascertain the breeding male flower production, respectively; and (d) fruit system of G. epetiolata. production phase: time elapsed between the end of the pistillate phase and fruit maturation. Fruit de- MATERIALS AND METHODS velopment was further divided into three stages: young, green, and ripe. STUDYswclm.-Geonoma epetiohta is an understo- We also recorded mean daily staminate flower ry palm that is restricted to mature forests on the production per inflorescence and flower longevity Caribbean slopes of Costa Rica and Panama (Hen- for each of 50 individuals that were observed twice derson et al. 1995). In Costa Rica, it is currently a day for four weeks. We estimated the mean num- found on a strip of land located between lowland ber of pistillate flowers produced per day by divid- and premontane rain forest (ca 50 km2) of the ing the total number of flowers in an inflorescence Central Mountain Range (Chazdon 1987); no oth- by the total number of days of the pistillate phase. er populations have been located between this area Receptivity of pistillate flowers was determined by and northern Panama. Much of the habitat where applying 3 percent H202 on stigmas of various G. epetiolata occurred has been lost or fragmented ages (1-20 d; Kearns & Inouye 1993). due to deforestation and the only large protected To determine the floral sex ratio per inflores- area where this species is found is the Braulio Car- cence, we counted the total number of staminate rillo National Park in Costa Rica (Fig. l). and pistillate flowers on 20 inflorescences of dif- Geonoma epetiolata has solitary stems and at- ferent plants. Each inflorescence was covered with tains a maxiinurn height of 2.5 m. The young a mesh net bag and the fallen staminate flowers 598 Marten and Quesada FIGURE 1. Geographic distribution of Geonomu epetiolatu in Costa Rica. Top right: map of Costa Rica with Braulio Carrillo National Park in the center. Left: Area of Braulio Carrillo National Park where G. epetiolatu is found. were counted every two weeks throughout the The frequency of flowering, measured as the flowering period. Pistillate flowers were counted di- number of inflorescences produced per year per in- rectly on the inflorescence because they do not fall dividual, was correlated with plant age and size us- until the fruits begin to develop. ing Spearman’s correlation tests. The degree of overlap (measured as the number of times pistillate REPRODUCTIVEPHENOLOGY.-TO study the flower- and staminate inflorescences overlapped within a ing and fruiting phenology of G. epetiolata, we used plant divided by the number of pistillate inflores- 102 reproductive plants and recorded the following cences produced) was also correlated with plant age reproductive parameters in each individual every and size.