Morphology of Gametophytes and Young Sporophytes of Sphaeropteris lepifera

Abstract

-Sphaeropteris lepifera is one of the largest tree ferns in Taiwan. On average, it produces 50.7 sporangia per sorus, and 64 spores per sporangium. Spore germination, after 2 years of storage at 4?C was over 95%. The pattern of spore germination was Cyathea-type, and the gametophytes exhibited mainly Drynaria-type development with occasional Adiantum-type development. Typical gametophytes were heart-shaped but had the potential to elongate and become elliptical. Multicellular hairs on the dorsal and ventral surfaces of the midrib cushion increased in size and changed shape with age. They were usually uniseriate when young, and became multiseriate with age. Gametophytes initiated antheridia about 1 month after spores were sown, and did not become hermaphrodites until 7 weeks later. During ontogeny, the gametangial sequence was from the male to hermaphroditic. Antheridia formed on the wings of the ventral and dorsal surfaces of gametophytes. The wall of each antheridium was composed of 5 cells. Archegonia appeared on the cushion of the ventral surface of gametophytes. Some gametophytes initiated clone-formation through vegetative regeneration. When sufficient water was provided, young sporophytes began to appear 12 weeks after spores were sown. The first fronds were midribless. The uniseriate, multicellular hairs on young sporophytes were similar to those on gametophytes. Gametophyte morphology, including mature forms, spore germination, and types of early development, trichomes, and gametangia, have been used to characterize fern taxa (Stokey, 1918, 1930; Atkinson and Stokey, 1964; Nayar and Kaur, 1971; Atkinson, 1973). These characteristics provide information relevant to fern phylogeny (e.g., Nayar and Kaur, 1971) and the ecology and reproductive biology of different species (Chiou and Farrar, 1997a, b; Chiou et al., 1998; Masuyama, 1975a, b, 1979). In the Cyatheaceae, spore germination is Cyathea-type and gametophyte development is Adiantum-type or nearly Drynaria-type (Nayar and Kaur, 1971). Gametophytes are long-lived (2-6 years) and tend to elongate slightly with age. The multicellular, bristle-like hairs that appear on gametophytes in this family indicate the Cyathaceae is phylogenetically close to the Loxsomaceae (Atkinson and Stokey, 1964). Antheridia and archegonia typically occur on the same gametophytes, with some vigorous gametophytes being strictly archegonial (Stokey, 1930). Apogamy was reported in some species in the Cyatheaceae 1 Corresponding author. This content downloaded from 157.55.39.231 on Wed, 05 Oct 2016 04:13:14 UTC All use subject to http://about.jstor.org/terms AMERICAN FERN JOURNAL: VOLUME 90 NUMBER 4 (2000) TABLE 1. Spore sources, usage, culture medium and storage period.