Adiantum

Adiantum (/ˌædiˈæntəm/),^[1] the maidenhair fern (not to be confused with the similar-looking maidenhair spleenwort fern), is a genus of about 250 species of ferns in the subfamily Vittarioideae of the family Pteridaceae,^[2] though some researchers place it in its own family, Adiantaceae. The genus name comes from Greek, meaning "unwetted", referring to the fronds' ability to shed water without becoming wet.

Description

They are distinctive in appearance, with dark, often black stipes and rachises, and bright green, often delicately cut leaf tissue. The sori are borne submarginally, and are covered by reflexed flaps of leaf tissue which resemble indusia. Dimorphism between sterile and fertile fronds is generally subtle.

They generally prefer humus-rich, moist, well-drained sites, ranging from bottomland soils to vertical rock walls. Many species are especially known for growing on rock walls around waterfalls and water seepage areas.

The highest species diversity is in the Andes. Fairly high diversity also occurs in eastern Asia, with nearly 40 species in China.

Species native to North America include A. pedatum (five-fingered fern) and the closely related A. aleuticum, which are distinctive in having a bifurcating frond that radiates pinnae on one side only. The cosmopolitan A. capillus-veneris (Venus-hair fern) has a native distribution that extends into the eastern continent. A. jordanii (California Maidenhair) is native to the west coast.

There is a rich Adiantum flora in New Zealand with 3 endemic species (A. cunninghamii, A. viridescens and A. fulvum) in a total of 10 recorded species. Many of these are common especially in the west and south of the islands.

Cladistics

It is now known that this genus is paraphyletic, and that the vittarioid ferns are derived from this larger paraphyletic genus. However, if Adiantum raddianum, and possibly a few other species, are removed, the remaining plants (genus type: Adiantum capillus-veneris) are then monophyletic.

Cultivation

Many species are grown in the horticultural trade. There are a number of tropical species, including A. raddianum and A. peruvianum. Both A. pedatum and A. aleuticum are hardy to zone 3, and are by far the most cold-hardy members of the genus. A. venustum is also cold-hardy to zone 5. A. capillus-veneris is hardy to zone 7. Hybrids, such as Adiantum × mairisii, are also popular.

List of species

Gallery

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  Rough Maidenhair Fern (Adiantum hispidulum)

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  Adiantum cunninghamii showing characteristic inrolled leaf margin containing sori

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  Adiantum lunulatum in Goa, India.

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  Delta Maidenhair (Adiantum raddianum)

References

• Germplasm Resources Information Network: Adiantum
• Flora of North America: Adiantum
• Flora of China: Adiantum species list