A reinvestigation of the morphology of the gametophyte and juvenile sporophyte of Ceratopteris thalictroides

Abstract

The spores of Ceratopteris thalictroides are large (104 × 128 μ), trilete, with a costate exine and devoid of perine. At germination a rhizoid is produced at the proximal pole, followed by a short uniseriate germ filament lateral to it. Formation of a prothallial plate is initiated by longitudinal divisions in the intercalary cells of the germ filament, and soon a strap-like plate is developed. The thallus broadens and becomes spatulate, but is devoid of any meristem. A pluricellular meristem is later differentiated from lateral marginal cells on one side of the thallus away from the anterior region. The meristematic region becomes notched and later cordate. The anterior half of the thallus expands and develops into a broad flat wing while a smaller, often uplifted wing is developed posterior to the meristem. A midrib is formed behind the meristem when the prothalli are ca. 5 weeks old. The mature prothallus is devoid of trichomes, asymmetrically cordate, with a large, spreading wing and a smaller, often curled and cornucopia-shaped wing lifted up from the substratum. The midrib is thin and bears rhizoids and archegonia on the lower surface. Antheridia are restricted to the wings and are common marginally; they are embedded in the prothallial tissue, and consist of a central mass of spermatozoids surrounded by a basket-shaped, thin, basal cell, a narrow ring cell, and a solitary disk-shaped cap cell. The latter opens like a lid at antheridial dehiscence. The first wall formed in the antheridial initial is basket-shaped and the second wall is nearly flat. Development of the embryo is of the common type in leptosporangiate ferns. The first juvenile leaf is naked, with a spatulate lamina supplied by a solitary vein, and associated with the first root. One or two thick multicellular hairs are produced at the base of the second leaf and, in the succeeding leaves, these appendages are palea-like. A stem apex becomes evident usually only after the fourth leaf is developed. All early juvenile leaves are subsessile with entire lamina. The venation becomes reticulate in the second or third juvenile leaf. It is concluded that Ceratopteris is more closely allied to Anemia and Mohria than to other genera of ferns.

Comparative development of heavily asymmetric-cordate gametophytes of Anemia phyllitidis (Anemiaceae) focusing on meristem behavior

“…Therefore, loss of a functional apical cell may influence the site change of the multicellular meristem in A. phyllitidis gametophytes. Similar site shifting of the multicellular meristem associated with absence of a typical apical cell is found in asymmetric gametophytes of other taxa, such as Ceratopteris (Nayar and Kaur 1969b;Pal and Pal 1963;Banks et al 1993;Banks 1999), Acrostichum (Nayar and Kazmi 1963), and Onychium (Nayar and Kaur 1971), all of which are distantly related in phylogeny (Smith et al 2006). This implies that the apical cell is probably involved in initiation site location of the multicellular meristem in cordate gametophytes.…”

“…Asymmetric cordate gametophytes have been reported in distantly related clades: Ceratopteris (Ceratopteridaceae, Nayar and Kaur 1969b;Pal and Pal 1963;Nester and Schedlbaur 1981;Nester 1985;Banks 1999;Banks et al 1993), Anemia and Mohria (Anemiaceae, Twiss 1910;Momose 1949;Atkinson 1960Atkinson , 1962Pray 1971), Onychium (Adiantaceae, Momose 1967;Nayar and Kaur 1971), and Acrostichum (Pteridaceae, Nayar and Kazmi 1964). Such asymmetrical cordate gametophytes have been classified into the Ceratopteris type of development by Nayar and Kaur (1971); an obconical meristematic cell (apical cell) that is necessary for typical cordate gametophytes never forms, and a multicellular meristem contributing to a cushion separately arises from the lateral side of the young gametophyte.…”

Embryology of Ceratopteris richardii (Pteridaceae, tribe Ceratopterideae), with emphasis on placental development

“…The presence of Golgi and dense ER in the distal-most hair cells in C. richardii support a secretory function, presumably mucilage is released to protect the SAM from desiccation after the first leaf ruptures the calyptra. In contrast to early shoot apical cell formation observed in the present study, Nayar and Kaur (1969) concluded the apical cell in C. thalictroides derives from the base of the first leaf after calyptral rupture.…”

“…In general, these divisions may be either parallel (Hofmiester 1862;Campbell 1893Campbell , 1936Conard 1908;Higinbotham 1941;Ward 1954;Jayasekera and Bell 1959;Nayar and Kaur 1969) or transverse (Leitgeb 1880;Rogers 1926;Cross 1931;Wardlaw 1955) with respect to the gametophyte plane. A second series of divisions in each quadrant produces octant cells in two tiers of four cells.…”

“…The first leaf in some leptosporangiate ferns was reported to originate from a tetrahedral apical cell followed by growth along a marginal meristem (Campbell 1895;Ward 1954;DeMaggio 1961). In other leptosporangiates, the first leaf originates directly from a marginal meristem (Nayar and Kaur 1969) or from one or two lenticular cells that proliferate to form many apical initials (Campbell 1895(Campbell , 1936(Campbell , 1908Conard 1908).…”