Reproductive traits of Pteris cadieri and P. grevilleana in Taiwan: Implications for their hybrid origin

Pteris cadieri (Pteridaceae) exhibits significant morphological variation, its fronds range from simply pinnate to bipinnatifid. The morphological characteristics of P. cadieri and P. grevilleana vary along a continuum and suggest that P. cadieri is a hybrid species and P. grevilleana is a potential parent species. However, previous studies do not provide evidence to support or refute this hypothesis. To explore this hypothesis of hybrid origin, the reproductive biology of P. cadieri and P. grevilleana was studied in Taiwan. There were diploid and triploid P. cadieri, but P. grevilleana was diploid. All plants of both species were apogamous. In both species, spore shape varied (tetrahedral, globose, ellipsoidal) and germination rate varied, the first frond of some juvenile sporophytes had a midrib, and polyembryony occasionally occurred, the latter being the first report of polyembryony in apogmous ferns. Variation in spore number per sporangium, spore size and spore shape indicated abnormal sporogenesis. All these traits suggested that P. cadieri and P. grevilleana are of hybrid origins. However, the hypothesis that P. grevilleana is a parent of P. cadieri should be reconsidered.