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

There are two varieties of Pteris fauriei in Taiwan: var. fauriei and var. minor. Their mature sporophytes are virtually indistinguishable based on gross morphology. To better understand these two varieties of P. fauriei 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 exhibits 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 P. fauriei var. fauriei is triploid. Diploid sporophytes produced 64–spore sporangia. Their haploid gametophytes produced archegonia, and antheridia that contain 64 sperm each. Gametophytes cultured for 10 weeks formed sexual sporophytes. The first fronds were midribless. Triploid sporophytes produced 32-spore sporangia. Triploid spores were significantly larger in diameter than haploid spores. Triploid gametophytes did not produce archegonia. They 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.

台湾地区分布有傅氏凤尾蕨（Pteris fauriei）的两个变种：傅氏凤尾蕨原变种（Pteris fauriei var. fauriei）与小羽傅氏凤尾蕨（Pteris fauriei var. minor）。二者的成熟孢子体（sporophyte）仅凭大体形态几乎无法区分。为深入解析该物种的两个变种及其间差异，并明确二者是否具有不同的倍性，我们对两个变种的孢子体与配子体（gametophyte）开展了细致的观察与比较研究。每个变种均具备独特且稳定的隐蔽性状（cryptic characteristics）与细胞型（cytotype）。基于模式标本孢子的直径，我们确认小羽傅氏凤尾蕨为二倍体，傅氏凤尾蕨原变种为三倍体。二倍体孢子体可产生含64枚孢子的孢子囊（sporangium，复数sporangia）；其单倍体配子体可形成颈卵器（archegonium，复数archegonia），以及每个内含64枚精子的精子器（antheridium，复数antheridia）。培养10周后，配子体便可产生有性孢子体，其首枚羽叶（frond）无中脉。三倍体孢子体则产生含32枚孢子的孢子囊。三倍体孢子的直径显著大于单倍体孢子。三倍体配子体无法形成颈卵器，但可产生含32枚精子的精子器，其直径显著大于单倍体配子体产生的精子器。三倍体配子体的寿命较单倍体配子体短4周。培养6周后，无融合生殖（apomictic）的三倍体孢子体直接从配子体细胞中产生，其首枚羽叶具3枚羽片（pinna）且带有中脉。本研究数据可为傅氏凤尾蕨原变种与小羽傅氏凤尾蕨的分类界定提供有效依据。