Cryptic characteristics distinguish diploid and triploid varieties of Pteris fauriei (Pteridaceae)

Abstract

There are two varieties of Pteris fauriei Hieron. in Taiwan: P. fauriei var. fauriei and P. fauriei var. minor Hieron. Their mature sporophytes are virtually indistinguishable based on gross morphology. To better understand these two varieties and the differences between them, and to determine whether they are based on different ploidies, we examined and compared the sporophytes and gametophytes of both varieties in detail. Each variety exhibited distinct, constant cryptic characteristics and cytotype. Based on the diameter of spores from type specimens, we confirmed that P. fauriei var. minor is diploid and that P. fauriei var. fauriei is triploid. Diploid sporophytes produced 64-spore sporangia. Their haploid gametophytes produced archegonia and antheridia containing 64 sperm each. Gametophytes cultured for 10 weeks formed sexual sporophytes, the first fronds of which lacked midribs. Triploid sporophytes produced 32-spore sporangia. Triploid spores were significantly larger in diameter than haploid spores. Triploid gametophytes did not produce archegonia but did produce 32-sperm antheridia, which were significantly larger in diameter than antheridia produced by haploid gametophytes. The life span of triploid gametophytes was 4 weeks shorter than that of haploid gametophytes. After 6 weeks in culture, apomictic triploid sporophytes arose directly from gametophyte cells. Each of their first fronds had three pinnae and a midrib. These data are useful for delimiting P. fauriei var. fauriei and P. fauriei var. minor.