The evolution, morphology, and development of fern leaves

Abstract

Leaves are lateral determinate structures formed in a predictable sequence (phyllotaxy) on the flanks of an indeterminate shoot apical meristem. The origin and evolution of leaves in vascular plants has been widely debated. Being the main conspicuous organ of nearly all vascular plants and often easy to recognize as such, it seems surprising that leaves have had multiple origins. For decades, morphologists, anatomists, paleobotanists, and systematists have contributed data to this debate. More recently, molecular genetic studies have provided insight into leaf evolution and development mainly within angiosperms and, to a lesser extent, lycophytes. There has been recent interest in extending leaf evolutionary developmental studies to other species and lineages, particularly in lycophytes and ferns. Therefore, a review of fern leaf morphology, evolution and development is timely. Here we discuss the theories of leaf evolution in ferns, morphology, and diversity of fern leaves, and experimental results of fern leaf development. We summarize what is known about the molecular genetics of fern leaf development and what future studies might tell us about the evolution of fern leaf development.

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

“…In horsetails, leaf arrangement is independent of segmentation pattern [41]. Leaves are reduced, discernible as the teeth of the stem sheath, and arranged in regular whorls, ranging from 4 to 12 elements (e.g., E. arvense) [26,[41][42][43] or to 36 elements (e.g., E. telmateia) [43] per whorl. The number of sheath teeth differs among Equisetum species and vary within a particular shoot, between successive whorls [42,43].…”

“…In Isoëtales, the SAM contains one (or two) AC or, alternatively, one group of superficial initials [17,19,24], depending on the age of the plant [25]. Unique to the lycophytes is the presence of microphylls, an evolutionary distinct type of leaf [16,19,24,26] that is initiated by one or two superficial cells in the peripheral zone of the meristem [18,22,27]. In Selaginella, in the SAM with distinct AC, microphylls develop in derivative segments with no particular correlation to the segmentation pattern [28].…”

General Features of Pteridophytes (Fern)

“…Recently the morphological and phylogenetic study was done which indicates that ferns are the sister group of seed plants (Vasco et al, 2013 andPrayer et al, 2001). The most important dissimilarities between the pteridophytes and the reminder of the vascular plants is that the ferns and their allies do not produce large floral or reproductive structures that give rise to seeds which eventually develop into the next generation of plants (Craft., 1999).…”

Mesozoic gymnosperms: megafloral changes through the Triassic–Jurassic of Eastern Gondwana

“…More generally, pinnate morphological terminology follows Andrews (1990, pp. xiii-xx) and Vasco et al (2013).…”