Bommeria is a small genus of rock ferns in the family Pteridaceae (order Polypodiales), native to the New World, with its range centered in Mexico and extending into the southwestern United States. The genus comprises only a handful of species, all small in stature and adapted to rocky, often arid habitats.
Morphologically, Bommeria is classified as a gymnogrammoid fern, meaning its spore-producing structures (sori) are unprotected and run along the veins on the undersides of the fronds. This arrangement stands in contrast to most other members of Pteridaceae, which typically bear linear, marginal sori protected by an indusium or a reflexed leaf-margin flap. The leaf stems (stipes) and fronds are hairy on both surfaces: short, sharp hairs appear on the upper surface, while the lower surface bears hairs that may be straight or curled, along with small scales.
Molecular phylogenetic studies have positioned Bommeria as a stem-group clade branching off at the base of the cheilanthoid ferns within Pteridaceae — more basal than the bulk of that group but less so than Doryopteris. Despite superficial similarities in soral arrangement, Bommeria is not closely related to Hemionitis, which was once considered its nearest relative; genetic analysis has demonstrated that Hemionitis is a more derived genus. Unusually for a family where many historically recognised genera have proven paraphyletic, Bommeria appears to be genuinely monophyletic. The basal chromosome number is 2n=60 (n=30).
Etymology
The genus name Bommeria honors Jean-Édouard Bommer (1829–1895), a Belgian botanist known for his work on ferns and lower plants.
Distribution
Bommeria is native to the New World, with its primary distribution in Mexico and reaching into the arid and semi-arid regions of the southwestern United States. Species tend to grow on rocky substrates, often on canyon walls or cliff faces.
Taxonomy Notes
Bommeria belongs to family Pteridaceae, order Polypodiales, and has been placed phylogenetically as a stem-group clade at the base of the cheilanthoid ferns — more basal than most cheilanthoids but less so than Doryopteris. It was historically allied with Hemionitis on the basis of shared gymnogrammoid soral morphology, but molecular data show this resemblance is homoplastic rather than indicative of close relationship. Unlike many Pteridaceae genera shown to be paraphyletic, Bommeria appears to be a natural (monophyletic) group. Chromosome base number: 2n=60 (n=30).
