Botrypus is a monotypic genus of perennial fern in the adder's-tongue family (Ophioglossaceae, order Ophioglossales, class Equisetopsida), containing the single species Botrypus virginianus (formerly Botrychium virginianum), commonly known as rattlesnake fern. It is a low-growing plant, typically 30 cm or less in height. The leaf is roughly triangular, 15–50 cm in size, held approximately parallel to the ground, and is 3–4 times pinnately compound with a bright green, soft texture. The round stem is bicolored — pinkish or light tan at the base and greenish nearer the branches. The fern has dimorphic fronds: a sterile leaf arises halfway up the stalk while the fertile leaf bearing sporangia is positioned at the tip. Spores are shed in late spring; the leaf emerges in early spring and senesces in late summer. The diploid chromosome number is 184.
Taxonomically, Botrypus was traditionally placed within Botrychium (subgenus Osmundopteris) but is now recognized as a distinct genus by the Pteridophyte Phylogeny Group (PPG I, 2016). Molecular phylogenetic research has established that it is sister to all other botrychioid ferns. A notable genetic feature is the presence of horizontally transferred mitochondrial DNA from a member of the Santalales (possibly mistletoe), making its mitochondria a genetic chimera. The species was first formally described by Linnaeus in 1753 as Osmunda virginiana.
Etymology
The common name "rattlesnake fern" derives from the plant's tendency to grow in habitats where rattlesnakes are also found in North America. The origin of the genus name Botrypus is not explained in the consulted sources.
Distribution
Botrypus virginianus is a wide-ranging fern found in many parts of the United States, the mountains of Mexico, Australia, parts of Asia including the Himalaya Mountains, and disjunctly in northern Europe — Norway, the Karelia region of Finland and Russia, and around the Gulf of Bothnia. It is notably absent from the rest of Europe.
Ecology
Rattlesnake fern grows in rich, moist woods in dense shade and does not tolerate direct sunlight. The leaf emerges in early spring and senesces by late summer, with spores shed in late spring.
Taxonomy
Botrypus is recognized as a distinct genus within Ophioglossaceae by the Pteridophyte Phylogeny Group classification of 2016 (PPG I), after previously being lumped into Botrychium in several earlier classifications (Smith et al. 2006; Christenhusz et al. 2011; Christenhusz & Chase 2014). Molecular phylogenetics places it as sister to all other botrychioid ferns. A unique feature is the horizontal transfer of mitochondrial DNA from a Santalales member (possibly mistletoe) into this fern's mitochondrial genome. Linnaeus first described the species in 1753 as Osmunda virginiana.
Cultural Uses
The fern has been used medicinally in India to treat dysentery. In the Himalayas, the large, succulent fronds are boiled and eaten. In the southern Appalachian Mountains of the United States, wild ginseng hunters use B. virginianum as an indicator species for locating American ginseng, giving rise to local names such as sang-find, 'seng sign, and 'seng pointer.
