Adiantum raddianum

Adiantum raddianum.

The Delta maidenhair fern is also known as Adiantum cuneatum.
It is seen classified in its own family Adiantaceae and also in Family Pteridaceae > Subfamily Vittarioideae.
A. raddianum and its numerous cultivars are popular indoor plants.

These grow in dense clusters on soil or rock.
Creeping, branching rhizomes, with brown scales, form dense masses.
The delicate, fan-shaped fronds are erect then arching.

Frond stalks, up to 25 cm long, are thin, shiny and almost black.
The complicated branching method is variously described as palmate or 3 or 4 pinnate.

Sterile and fertile fronds are very similar.
The blade, which ages from light to dark green, is up to 25 cm long by 15 cm wide.
The surface of the smooth, hairless leaf blades is unwettable – most water runs off and the
    little that may remain is in the form of discrete droplets.

Leaflets, with or without a short stalk, have straight sides and a curved, lobed end.
The lobed appearance is due to modified sections of the leaflet margin forming flaps that are folded
    underneath and bear the sporangia (soral flaps or false indusia).

The flaps, which resemble indusia are diagnositc for Adiantum species.

The pale green or brown flaps are round or kidney-shaped and about 1.5 mm across.
Spores are yellowish.

J.F.