Self-and Cross-Pollination of Encyclia cordigera (Orchidaceae) in Santa Rosa National Park, Costa Rica

Abstract

The epiphytic deciduous forest orchid Encyclia cordigera was manually self-pollinated, out-crossed against one other parent, and out-crossed against a maximum number of other parents in Santa Rosa National Park, Costa Rica. There was no difference in the percent inflorescences that set fruit between selfed and single-parent out-crossed plants, and on the inflorescences that set fruit there was no difference in the percent flowers that bore fruit (85 to 92% for 119 and 82 flowers). However, only 5 percent of the multiple-fathered inflorescences failed to set some fruit, and 97 percent of the flowers set fruit; these values are significantly different from those for the selfed plants and flowers. The overall percent of inflorescences that bore fruit and the percent flowers that bore fruit was very much greater on the hand-pollinated plants than on the unmanipulated ones growing only a few meters away. This finding may indicate that fruit set by E. cordigera is pollinator limited, but other interpretations are given. Is Encyclia cordigera (ORCHIDACEAE) SELF-INCOMPATIBLE and does the number of fathers for a plant's fruit crop influence the size of that fruit crop? E. cordigera is a common epiphytic orchid in the deciduous forest lowlands of Guanacaste Province, Costa Rica. It is especially common in Crescentia alata trees in the flat plateaus in the center of Santa Rosa National Park (SRNP), where this study was conducted. Large numbers of these orchids flower from late February to late March (mid-dry season). E. cordigera flowers are produced 1-13 per inflorescence, and those on one inflorescence open during a period of about one week. If not pollinated or relieved of pollinia, the flowers last at least 10 days. Once pollinated, the white portions of the petals turn yellow and the ovary begins to swell. In nature, mediumto large-sized black female carpenter bees (Xylocopa spp.) enter the flowers in search of nectar and receive the viscidium on the frons or top of the head; the bright yellow pollinia are then later stripped off on the stigma of another flower. The three petals of the flower and the column are colored white and lavender, and shaped such that they are very similar to the flower of Gliricidia sepium, a common legume tree that is heavily visited by these 72 BIOTROPICA 12(1): 72-74 1980 same bees for nectar at the time E. cordigera is in bloom. MATERIALS AND METHODS All orchids were relieved of their pollinaria by sticking the pointed end of a ball-point pen cap or clip into the flower and then withdrawing it with an upward motion. The sticky viscidium readily adhered to the plastic surface. The cap over the four pollinia was knocked off, and in the case of self-pollinated flowers, the pollinia were then placed on the sticky stigma. In outcrossed flowers, the pollinia were carried to another plant and placed on the stigma of a flower that had already been relieved of its pollinaria by the experimenter. Only inflorescences with intact and unpollinated open flowers were used, and all flowers on a test inflorescence were pollinated. Occasionally during transfer one of the four pollinia would fall off, but usually all four pollinia were placed in contact with the stigma. Outcrossed inflorescences were of two types. Single father inflorescences had all their flowers pollinated by pollinia brought from a single other parent (and usually the other parent received the pollinia from the plant that received its pollinia). This content downloaded from 207.46.13.127 on Fri, 14 Oct 2016 04:07:12 UTC All use subject to http://about.jstor.org/terms Multiple father inflorescences had each flower on the inflorescence pollinated by pollinia from a different pollen donor: if there were n flowers on the plant, that plant's clutch had n fathers. Within 24 hours after pollination, the stigmatic surface of a pollinated E. cordigera flower swells to engulf the pollinia and is no longer sticky, so that we have assumed that none of the flowers were subsequently pollinated by bees after the experiment. Flowers of E. cordigera do not self-pollinate if the pollinia are not physically moved to the stigma by an outside