Pitcairnioideae

Septicidal capsules derived from fully superior to inferior ovaries and medium-sized to small seeds suggest relatively uncomplicated, mechanical dispersal for most Pitcairnioideae. Membranous or hair-like extensions of the outer integument of the seed often promote buoyancy, except for Navia that alone lacks a two-layered testa (Fig. 3.9). Occasional arrangements suggest extraordinary functions. Gross (1993) assigned the spongy, textured wing of Pitcairnia aphelandri'ora, a bushy species described from along the Napo River in Ecuador, and Pepinia punicea importance for water transport a reasonable supposition that warrants testing.

Zoochory seems less likely among Pitcairnioideae, although cryptic elaiosomes like those attached to the dry seeds of other myrmecochorous ora may turn up yet. Rodents present another possibility if wild relatives share the partiality domesticated guinea pigs exhibit for certain Pitcairnia and Puya seeds. Diverse shapes and sizes, which exceed those of Tillandsioideae and most Bromelioideae (although delivery in a berry complicates comparisons on this second count), suggest multiple dispersal mechanisms and diverse rooting media. Whatever its biological basis, seed form circumscribes several genera enough to serve as a taxonomic marker. Pitcairnia seeds, for example, possess hair-like projections from both ends of the testa, while those of closely related Pepinia bear a wing more reminiscent of Puya (Fig. 3.9).

The occasional epiphyte (all facultative; e.g., Pitcairnia heterophylla, Brocchinia tatei) possesses arguably the most airworthy seeds in the subfamily. Conversely, low seed mobility elsewhere helps explain the often clumped dispersions and fragmented populations of certain terrestrials (e.g., Andean Puya species; Fig. 9.2). However, rather ordinary morphology need not preclude long-range dispersal. Pitcairnia, for example, ranks among the most widely distributed of the bromeliad genera, and P. feliciana alone illustrates the successful outcome of a transoceanic dispersal (Fig. 1.1). Insularity, mostly on tepuis, like isolation on oceanic islands, possibly favored the unappendaged and probably short-ranged seeds of Navia.

Although basically terrestrial, Pitcairnioideae exploit a variety of kinds of soils and, quite often, less accommodating substrates like precipitous rocky cliffs (e.g., various Hechtia, Navia, Pitcairnia; Fig. 7.1B). Perhaps the myriad shapes and sizes (six major classes; Fig. 3.9) of the seeds that characterize this subfamily partly re ect the microtopography of rooting media, which for the saxicoles may parallel the lithology of colonized outcrops. Brocchinia (Fig. 6.1D) offers extraordinary opportunity to match bromeliad seeds with speci c kinds of substrates because its fewer than 20 species colonize bark, soil and rocks alone or interchangeably. Data on seed longevity and requirements for germination (e.g., light) would complement those ndings.

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