Seeds of Puerto Rican Trees and Shrubs: Second Installment

During the 1940’s, scientists at the Tropical Forestry Experiment Station (now the International Institute of Tropical Forestry) carried on an active program of forest tree seed research. Their effort resulted in a published summary of the data gathered (Marrero 1949). Seed weights and/or germination data were recorded for 128 species, the majority of which were exotics imported for adaptability tests in Puerto Rico. Although the work represents only a small portion of the more than 850 native and naturalized tree species in Puerto Rico, it remains a valuable reference. The fruits and seeds were collected by a variety of methods. Many were gathered from the ground under seed-bearing trees or clipped from fruit-laden branches with pruning poles. For some species, a number of parent trees and sites are represented; however, a small number of trees on a single site were the source for most species. Replication was generally not possible due to the limited time available for collections and because a number of species are rare and seldom seen bearing seeds. When fruits were collected, they were weighed immediately or kept refrigerated until weighing could be done. The seeds were separated from the fruits by hand or by screening for the small quantities needed for research and exchange programs. Many tropical plant species have recalcitrant seeds (those that cannot withstand drying); therefore, each species was evaluated as to how much air-drying its seeds could tolerate. Seeds of most of the species collected were dried in front of an air conditioner for a few hours to 2 or 3 days. Hard-seeded legumes and species with similar seeds were dried in a solar drier. In the course of collecting seeds for international exchange, and as necessary data for silvical descriptions, additional data on the seeds of native Puerto Rican trees and shrubs and naturalized exotics have been obtained. Air-dried seed weights, germination periods (time from sowing to first germination), and germination percentages have been obtained for 119 species in addition to the fruit weights for 34 of the species. Weights and germination percentages for a few of these species were also reported by Marrero (1949). The weights reported by Marrero agree fairly well with the weights obtained for this report. In most cases, the seeds were weighed individually on an analytical balance. However, very small seeds were generally weighed in groups of 100; all weights are given as number of seeds per kilogram. Some of the hard-coated seeds were scarified by nicking the seedcoat with a knife blade or a file. Germination was done at ambient temperature (24 to 30 “C) in one of three substrates: potting mix in trays, sand in trays, or moistened filter paper in petri dishes (blotter method). Time lapse from sowing until the first germination occurred (germination period) and the percentage of seeds finally germinating were noted.