Cauline meristems in leptosporangiate ferns: structure, lateral appendages, and branching

Abstract

HEBANT-MAURI, R. 1993. Cauline meristems in leptosporangiate ferns: structure, lateral appendages, and branching. Can.J. Bot. 71: 1612-1624. This study on shoot apical meristem structures in leptosporangiate ferns examines the precise initiation of lateral appendagcs in the meristems. Interrelationships and early development of the main stem, fronds, and branchcs are described. Ontogeny and histology within the apical meristem must be considered in a reasonable morphological interpretation of the adult plant, especially with respect to the lateral system (i.e. frond and bud assemblage) in creeping branched ferns.

Diversity of phyllotaxis in land plants in reference to the shoot apical meristem structure

“…Generally, the SAM of monilophytes contains a single AC, which is usually tetrahedral and distinct within the meristem, and derived segments [35][36][37]. The exceptions to this characteristic AC shape are members of the Salviniaceae family, which have a lenticular AC with two cutting surfaces, relating to the dorsiventral symmetry of the shoots [36,38].…”

“…The exceptions to this characteristic AC shape are members of the Salviniaceae family, which have a lenticular AC with two cutting surfaces, relating to the dorsiventral symmetry of the shoots [36,38]. Regardless of the shape, the AC divides parallel to the anticlinal sides and gives rise to segments (merophytes), which in species with relatively flat or concave apices are more rectangular and elongated, forming a distinct superficial layer of prismatic cells [36,37]. Interestingly, additional potential ACs, formed by the anticlinal oblique divisions can occur at the SAM surface in some filicalean ferns [35].…”

“…Leaves are formed in the merophytes by a constant sequence of divisions and can be in close clonal relationship to the successively cut segments, as, e.g., in Ceratopteris [36,37,39]. Typically, however, more than one merophyte is involved in leaf formation, and thus the impact of segmentation on the leaf spatial arrangement is less pronounced and strict, e.g., in Dicksonia, Osmunda [35][36][37]40].…”

“…Research and plant descriptions to date suggest a relatively small diversity of phyllotactic patterns within the monilophytes (e.g., [37]), but only several taxa have been intensively analyzed in this respect; their phyllotaxes are presented here.…”

“…Distichous phyllotaxis often occurs in ferns with a creeping rhizome. In such species, leaves are usually initiated in two ranks and form a true distichous pattern (leaves positioned 180° from one another, e.g., in Stromatopteris, Microgramma [37,44,45]) or its modification (successive leaves slightly shifted to the dorsal side with the circumferential distance between them less than 180°, as in Davallia [46]). Alternatively, tristichous pattern may be formed, such as in Lomagramma [47], or in some cases, only a single row of dorsal leaves develops in the rhizome [37].…”