Sceptridium, commonly known as the grape-ferns, is a genus of seedless vascular plants in the family Ophioglossaceae and order Ophioglossales. The genus comprises small, fleshy-rooted plants that reproduce via spores shed into the air rather than by seeds, placing them among the most ancient lineages of land plants.
Grape-ferns are closely allied to two related genera in the Ophioglossaceae: Botrychium (the moonworts) and Botrypus (the rattlesnake fern). Sceptridium is distinguished from Botrychium by possessing at least some entirely sterile fronds — in Botrychium, all fronds are spore-bearing — and by its bi- or tri-pinnate (twice or thrice divided) sterile fronds, whereas Botrychium fronds are singly pinnate, or rarely bipinnate. From Botrypus, Sceptridium differs in being evergreen or winter-green rather than deciduous, and in having the non-spore-bearing (trophophore) portion of the frond on a notably long stalk, as opposed to the short stalk found in Botrypus.
The taxonomic boundaries of Sceptridium have long been debated. Molecular phylogenetic work by Smith et al. (2006) led to Sceptridium being lumped into a broadly defined Botrychium, a treatment followed in the classifications of Christenhusz et al. (2011) and Christenhusz and Chase (2014). However, Sceptridium is restored as a distinct genus in the Pteridophyte Phylogeny Group I (PPG I) classification of 2016, which represents the current consensus among pteridophyte systematists.
Distribution
Sceptridium species occur across temperate and subtropical regions of both hemispheres. Members of the genus are found in North America, East Asia (including Japan), Australia, and the Neotropics, reflecting a broad distribution typical of ancient fern lineages. Individual species tend to occupy woodland and meadow habitats.
Ecology
Grape-ferns are small terrestrial plants of woodland floors, meadows, and disturbed grassy habitats. Like other members of Ophioglossaceae, they produce a single annual frond divided into a sterile vegetative portion (trophophore) and a fertile, spore-bearing portion (sporophore). The plants are evergreen or winter-green, remaining photosynthetically active through cooler months, which distinguishes them ecologically from the deciduous Botrypus.
Taxonomy Notes
Sceptridium has historically been treated as a subgenus of Botrychium, and molecular phylogenetic classifications (Smith et al. 2006; Christenhusz et al. 2011; Christenhusz & Chase 2014) continued to lump it within a broad Botrychium. The Pteridophyte Phylogeny Group (PPG I, 2016) restored it as a distinct genus within Ophioglossaceae, the treatment currently prevailing in modern pteridophyte taxonomy.
