Interpopulational Variation in the Gametophytes of Pellaea Andromedaefolia

Abstract

A B S T RAe T The development and mature morphology of the gametophytes from both sexual and apogamous populations of the fern Pellaea andromedaefolia were investigated. While most sexual examples wereIndistinguishable, some differences were noted. An insular collection was distinctive in its variability and irregularity of form. Although the latter was a representative of var. pubescens, other collections of the variety could not be distinguished from var. andromedaefolia on the basis of gametophytic characteristics. The apogarnous gametophytes were decidedly more variable in development and often very different from sexual thalli. The mature asexual thalli . tended to be more irregular in form and usually sharply divergent from the typical cordate type characteristic of the sexual populations. Each of the five apogamous samples was unique with respect to gametophyte development. The differences among the gametophytes of the various populations do not correlate with the sporophytic characteristics which differentiate the two varieties of the species.

A drought‐driven model for the evolution of obligate apomixis in ferns: evidence from pellaeids (Pteridaceae)

“…Among pellaeids, the apomictic cytotypes of Pellaea andromedifolia are thought to have originated recently based on their relative rarity (Tryon, 1968), and this group provides evidence suggesting how lineages curtail the production of functional archegonia. Although these young, geographically restricted lineages continue to produce some cordate gametophytes with some archegonia, the latter appear to be nonfunctional (Pray, 1968a). These archegoniate gametophytes mature slowly, making them noncompetitive with members of their cohort that produce sporophytes apogamously.…”

“…In each of these examples, the failure of apomictic gametophytes to produce archegonia is most likely due to heterochrony (Pryer and Hearn, 2009). Gametophytes of sexual pellaeids require several months to mature, proceeding through a series of developmental landmarks including phase a, an initial filamentous phase; phase b, formation of a two‐dimensional prothallium; phase c, initiation of a meristem leading to a classic cordate gametophyte; phase d, a unisexual phase defined by the protandrous development of antheridia; and phase e, the development of archegonia to attain bisexuality (Pray, 1968a, b, 1970).…”

Reproductive biology of isolated fern gametophytes

“…The following section presents a few examples to indicate that variation is possible and does occur among populations of the same species. Pray (1968) reported that sexual populations of Pellaea andromedaefolia differed in ganetophyte morphology.…”