Morphology of the gametophytes of some species of Pellaea and Notholaena

Abstract

SUMMARY Morphology of the spores, prothalli and juvenile leaves of 6 spp. of Pellaea. and 2 spp. of Notholaena is described. The spores are trilete and possess a crassimarginate laesura. The exine is psilate and there is a distinct psilate perine in Notholaena. In most species of Pellaea the exine is psilate, but there is a perinous ornamented outer layer closely adhering to it: the exine is spinulose and a perinous layer is absent in P. falcata and P. rotundifolia. The germ filament is composed of short, thick cells. A prothallial plate is formed by longitudinal divisions of the anterior cells when the germ filaments are 4–10 cells long. In some species, the terminal cells of the filament are sluggish and are often pushed aside by expansion of cells behind them. Young prothalli are usually ameristic but a sluggish obconical apical cell may be differentiated in some species. As the prothallus grows, the apex becomes notched and cordate. Cells behind the apical notch then constitute an apical meristem. Formation of a midrib is initiated when the prothalli are 5–6 weeks old. P. doniana, P. falcata and P. rotundifolia are sexually reproducing species and develop cordate naked prothalli with thin midribs bearing sex organs. The others are apogamous and the prothalli, soon after the development of a cordate apex, become irregular in shape. Apogamous development of the sporophyte is initiated by the formation of a multicellular cushion on the lower surface of the thallus, generally behind the apical notch: on highly lobed thalli the major lobes may develop a separate sporophyte on each. The cushion develops glandular hairs and paleae similar to those on the sporophyte and grows out as a flat, hood‐like protuberance in which a 3 ‐sided meristematic cell may soon be developed. The hood grows out as the 1st juvenile leaf and often a second leaf is soon developed near its base. A stem apex is differentiated by cells close to the leaf base and further leaves are formed. No roots are produced till the sporophyte develops 3 or 4 leaves. Vascular elements are developed in the apogamous cushion early in development and often extend into the prothallial tissue below. The lamina of the early juvenile leaves is nearly spatulate and entire or faintly lobed: it is naked in the first few leaves, but later, glandular hairs spread from the stipe upwards over the lamina.

Gametophyte development and reproduction of Argyrochosma nivea (Pteridaceae)

“…Apogamy is a common phenomenon in some of these cheilanthoid genera, and it is known to occur in Argyroshcosma, in both A. nivea here studied (Goebel 1905;Woronin 1907) and A. incana (Nayar & Bajpai 1963). The development pattern of the apogamous sporophytes in A. nivea observed here follows the general steps described previously for the species and for A. incana.…”

“…According to these authors, the Vittaria type of germination is the most common within the leptosporangiate ferns, including A. nivea, A. incana (Nayar & Bajpai 1963) The longitudinal division of the uniseriate filament of A. nivea occurs in the subapical cells, the apical one remaining quiescent until posterior stages. This is dissimilar to the process described for A. incana (Nayar & Bajpai 1963), but is identical at what has been observed in species of the related genus Astrolepis, as A. sinuata (Lag. ex Sw.) D.M.…”

“…Nevertheless, in A. nivea, as is has been stated by Atkinson (1973) for several genera of the Pteridaceae, it is difficult or impossible to determine the original position of the meristem looking to the adult gametophytes. Within cheilantoid ferns, Ceratopteris model of vegetative development seems to be infrequent, appearing in Astrolepis and Argyrochosma (Nayar & Bajpai 1963), and in Notholaena, Hemionitis and some Cheilanthes (Nayar & Kaur 1971).…”

“…Studies on the gametophyte morphology of members of the genus Argyrochosma are few, and we only found the simple report on that of A. incana (C. Presl) Windham (Nayar & Bajpai 1963, sub Notholaena incana C. Presl). Better known are the gametophytes of other species from related cheilanthoid genera.…”

“…Better known are the gametophytes of other species from related cheilanthoid genera. Besides others, we can point out the following works that primarily focus on the morphological description of gametophytes of Notholaena (Pray 1961;Nayar & Bajpai 1963), Pellaea (Hayes 1924;Nayar & Bajpai 1963;Tryon 1968) and Cheilanthes (Pray 1961;Nayar 1963;Pangua & Vega 1996;Gabriel y Galán & Prada 2009). …”