Scanning electron microscopy of gametophyte characters and antheridial opening in some Ceylonese species of Thelypteridaceae

Abstract

Gametophytes of the fern family Thelypteridaceae were cultivated aseptically under controlled conditions and investigated with the scanning electron microscope. This report concerns six species, viz. Sphaerostephanos arbuscula S. subtruncatus, S. unitus, Macrothelypteris torresiana, Amauropelta hakgalensis and Pneumatopteris truncata. The gametophytes have some features in common. They are more or less heart‐shaped and have glandular trichomes on surfaces and margins. In the middle is an elongated cushion bearing gametangia and rhizoids on the lower surface. Antheridia are of the type common to leptosporangiates, consisting of a basal cell, a ring cell and a cap cell. Archegonia consist externally of four rows of cells meeting at the top with triangular cells. The following features are distinguishing. The form of the margin of the thallus, type of hairiness, and the abundance of glandular hairs. Acicular hairs occur in Sphaerostephanos unitus and Pneumatopteris truncata. In Amauropelta hakgalensis the archegonium deviates from the common type in having a basal layer that consists of eight cells instead of four. In Macrothelypteris torresiana the four or three top cells are markedly irregular. In Sphaerostephanos arbuscula and Amauropelta hakgalensis the antheridial cap cell is sometimes divided. The manner of opening of antheridia and release of spermatozoids varies in each of the species investigated. This investigation reveals that it is possible to identify the species from gametophyte characters only.

Gametophytes of some Ceylonese species of Thelypteridaceae

“…Acicular hairs are rather uncommon among fern gametophytes, being restricted to the Grammatidaceae and the Thelypteridaceae (Nayar & Kaur 1971). They were found in 9 of the species investigated by me (7 of the 12 species described here and 2 of the 6 species described in Tigerschiold 1989 a). In Thelypteridaceae, to my knowledge, gametophyte acicular hairs have been reported in 9 of about 45 species investigated by different authors (Momose 1941;Nayar & Chandra 1963;Atkinson & Stokey 1964, 1973Mittra & Sen 1969;Atkinson 1971Atkinson , 1975.…”

“…Glandular hairs borne on a protruding cell or a uniseriate filament subtending the hair, as in Thelypteris confluens (Fig. 5 ) , were also found in Amauropelta hakgalensis (Tigerschiold 1989 a). According to Nayar & Kaur (1971) such structures occur in some profusely hairy species.…”

“…They are now kept in greenhouse at the Department of Botany in Stockholm. The methods for spore collection, cultivating, sampling, measurements and statistical treatment of glandular trichome length are described in Tigerschiold (1989 a). For conventional scanning electron microscopy a Cambridge 600 instrument was used.…”

Dehiscence of antheridia in thelypteroid ferns

“…The latter authors claimed that the mechanisms of antheridial opening are family-specific. In an earlier investigation on the gametophyte of 6 species of Thelypteridaceae, I made some observations on antheridial opening that were in conflict with traditional viewpoint (Tigerschiold 1989). During further investigations with the scanning EM of gametophytes of 12 additional species in the family, these observations have been extended.…”

Ultrastructural features of spermatocytes and spermatozoids in the fern Phyllitis scolopendrium (L.) Newm. subsp. scolopendrium

“…Arrowheads indicate possible amyloplast imprints in the last turn of the spiral. × 6000 v one side (Elmore and Adams 1976;Nester 1985;Tigerschiöld 1989;Kotenko 1990). This is not the case with P. scolopendrium spermatozoids which are released through limited laceration of the cap cell which remains joined to the ring cell below.…”