Abstract
This paper continues consideration of the spores of three paleotropical fern genera – Taenitis, Syngramma, and Austrogramme (Pteridoideae, Pteridaceae) from South-Eastern Asia and Oceania. At the second stage, we carried out a comparative scanning electron microscopy study of spores of three species of Austrogramme, four species of Syngramma, and six species of Taenitis and added information about previously studied spores of seven species of these genera. Spores of all examined species are trilete, tetrahedral or tetrahedral-globose with convex to hemispherical distal side and plane, convex or conical proximal side. The spores of Austrogramme species are the smallest, simplest in ornamentation and similar to each other. Sculpture of the proximal and distal sides are microverrucate, the surface of the spores is covered by granular deposits. Spores of most Syngrammaspecies are very similar to spores of Austrogramme species in shape and surface sculpture: their distal and proximal surfaces are microverrucate, whereas the spores of S. borneensis and S. cartilagidens have the low-tuberculate sculpture. Spores of Taenitis species are very different from the spores of Austrogramme and Syngramma. Seven of nine studied species have spores with well-expressed cingulum (T. blechnoides, T. cordata, T. diversifolia, T. interrupta, T. luzonica, T. obtusa, and T. requiniana), three species (T. cordata, T. hookeri, and T. pinnata) have spores with prominent laesural ridges. The spores have well-expressed ornamentation – tuberculate, baculate, rugate, tuberculate-rugate. The most conspicuous character of the ornamentation of spore surfaces is the presence of rodlets associated with sculpture elements. The densest rodlets are characteristic of Taenitis diversifolia, T. luzonica, T. obtusa, and T. requiniana. Spore size (equatorial diameter) ranges on average between 22 μm and 37 μm in Austrogramme, between 27 μm and 41 μm in Syngramma, and between 26 and 51 μm in Taenitis species.
Highlights
This paper continues consideration of spore morphology of three paleotropical fern genera – Taenitis Willd. ex Schkuhr, Syngramma J
The aim of this work is a comparative morphological study of the spores of Taenitis, Syngramma, and Austrogramme using scanning electron microscopy (SEM) and evaluation, whether the spore characteristics have the value for phylogeny of these genera
The results of this study confirm the diagnostic value of the spore morphology for the phylogeny and taxonomy of three fern genera – Austrogramme, Syngramma, and Taenitis
Summary
This paper continues consideration of spore morphology of three paleotropical fern genera – Taenitis Willd. ex Schkuhr, Syngramma J. Holttum (1975) was the first, who studied the relationship between Taenitis and Syngramma and considered them to the Gymnogrammeoid ferns. Different authors considered these three fern genera as belonging to the separate family Taenitidaceae Zhang et al (2015, 2017) classify these three genera to subfamily Pteridoideae C. Schuettp., family Pteridaceae and subfamily Pteridoideae Link sensu Zhang et al (2015). This system recognizes all three genera sensu Tryon et al (1990); each genus is considered as monophyletic (Taenitis and Austrogramme) (Cochran et al, 2014) or assumed to be monophyletic (Syngramma). Within Austrogramme, this system recognizes about six species, within Taenitis and Syngramma – about
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