Onocleaceae is a small family of terrestrial fern

Fern

A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...

s. There are four genera of onocleoids: Matteuccia, Onoclea, Onocleopsis

Onocleopsis

Onocleopsis is a genus of ferns in the family Onocleaceae containing only one extant species ....

, and Pentarhizidium

Pentarhizidium

Pentarhizidium is a genus of two Asian fern species. These species have formerly been included in Matteuccia or Onoclea. Recent genetic analysis has determined that these two species form a discrete clade that is basal to the rest of this fern group, and so have been located in their own genus. P...

, consisting of five species largely in north temperate climes.

Members of the family have the following characteristics, being distinguished by having strongly dimorphic frond

Frond

The term frond refers to a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group...

s, with the fertile fronds different from the sterile fronds. The rhizomes are long- to short-creeping to ascending, and sometimes stoloniferous (Matteuccia and Onocleopsis). The leaves are strongly dimorphic and the petioles

Petiole (botany)

In botany, the petiole is the stalk attaching the leaf blade to the stem. The petiole usually has the same internal structure as the stem. Outgrowths appearing on each side of the petiole are called stipules. Leaves lacking a petiole are called sessile, or clasping when they partly surround the...

 have two vascular bundles uniting distally into a gutter-shape. The blades are pinnatifid or pinnate-pinnatifid. The veins are free or anastomosing, lacking included veinlets. The spore

Spore

In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...

s are reniform, brownish to green. The sori are enclosed (sometimes tightly) by reflexed laminar margins, also with membranous, often fugacious true indusia.
.

Formerly, the two species in the genus Pentarhizidium were considered to be members of Matteuccia, but genetic analysis has determined that they compose a basal sister clade to the rest of the family. This family has been determined by genetic analysis to be closely allied to the Blechnaceae

Blechnaceae

Blechnaceae is a family of nine genera and between 240-260 species of ferns, with a cosmopolitan distribution.Most are ground dwelling, some are climbers, such as Stenochlaena. A characteristic feature of many species is that the young opening fronds are usually tinged with red.Genera*Blechnum L....

, within the clade of families sometimes known as Blechnales

Blechnales

Eupolypods II is a clade of ferns in the order Polypodiales.Although studies agree that the families in question are related to each other, classifications which define the order Polypodiales broadly include the Blechnales in that order...

 (which includes the athyrioid ferns and asplenioid ferns as well) (this clade is often treated as part of the order Polypodiales

Polypodiales

The order Polypodiales encompasses the major lineages of polypod ferns, which comprise more than 80% of today's fern species. They are found in many parts of the world including tropical, semitropical and temperate areas...

 however). Matteuccia struthiopteris was previously classified under the Dryopteridaceae

Dryopteridaceae

Dryopteridaceae, is a family of leptosporangiate ferns in the order Polypodiales. They are known colloquially as the wood ferns. They comprise about 1700 species and have a cosmopolitan distribution. They may be terrestrial, epipetric, hemiepiphytic, or epiphytic. Many are cultivated as...

, and still is by the USDA.

Species

Five species, in four genera

• Matteuccia struthiopteris (ostrich fern) - wide distribution including North America, Europe, and Asia
• Onoclea sensibilis (sensitive fern) - North America and eastern Asia, with the American and Asian populations being recognized as distinct varieties
• Onocleopsis hintonii - found in a restricted range of wet mountain canyons in southern Mexico and Guatemala; some botanists (especially Masahiro Kato) consider this to be a species of Matteuccia
• Pentarhizidium
  Pentarhizidium
  Pentarhizidium is a genus of two Asian fern species. These species have formerly been included in Matteuccia or Onoclea. Recent genetic analysis has determined that these two species form a discrete clade that is basal to the rest of this fern group, and so have been located in their own genus. P...
  
  

- Pentarhizidium orientalis - eastern Asia as far south as the Himalayas

Himalayas

The Himalaya Range or Himalaya Mountains Sanskrit: Devanagari: हिमालय, literally "abode of snow"), usually called the Himalayas or Himalaya for short, is a mountain range in Asia, separating the Indian subcontinent from the Tibetan Plateau...

- Pentarhizidium intermedia - China to India

Taxonomy

Probable Onocleaceae phylogeny (line lengths are not significant)