© 1987 Heron Publishing—Victoria, Canada
Ecophysiological characteristics of the seed of the tropical forest pioneer Urera caracasana (Urticaceae)
A. Orozco-Segovia, C. Vàzquez-Yanes, R. Coates-Estrada and N. Pérez-Nasser
Instituto de Biologia, UNAM, Apartado Postal 70-233, Deleg. Coyoacàn, 04510 Mèxico, D.F. / Received January 16, 1987
Summary
Urera caracasana (Jacq.) Griseb is a small, fast-growing evergreen pioneer tree which colonizes openings in the tropical rain forest of ‘Los
Tuxtlas’, Veracruz, Mèxico. Annual seed production by 10 trees was estimated to range from 0.4 × 105 to 1.6 × 106 seeds per tree. Fifteen species of resident and migratory birds were observed to visit the plants and disperse the seeds.
Most seeds imbibed in petri dishes placed on the forest floor beneath a small opening in the canopy, where the red/far-red
ratio of the light was around 1.0, germinated within 2 weeks. Germination beneath the forest canopy, where the red/far-red
ratio of the light was approximately 0.2, was much slower and did not exceed 40%. A minimum of 4 h daily exposure to unfiltered
natural light was required for rapid germination in the forest. In the laboratory rapid germination at 25 °C required a minimum
of 4 h white light. However, if temperature during the light period was 35 °C, 30 min exposure to white light daily was sufficient
to induce germination. Seeds that failed to germinate when imbibed for 60–360 days in petri dishes placed on the forest floor
beneath the forest canopy, germinated rapidly in the laboratory when held at 25 °C and exposed daily to 12 h white or red
light. Seeds imbibed for 120 days or more beneath the forest canopy were also induced to germinate by 12 h daily exposure
to far-red light when this was combined with a 35/25 °C day/night temperature regime.
Seeds buried in vermiculite-filled nylon mesh bags disappeared rapidly with few remaining after 2 months. Seeds that survived
remained viable and germinated when incubated in petri dishes at 25 °C. Initially, buried seeds required light for germination.
However, after 17 months’ burial, seeds germinated in darkness when transferred to the laboratory and incubated on agar at
25 °C.
