Lygodium microphyllum

Lygodium microphyllum.

Old World climbing fern, Climbing Maidenhair or Snake Fern.

Kingdom Plantae > Division Pteridophyta > Order Schizaeales.

Lygodium is usually seen in Family Schizaeaceae but sometimes in its own family Lygodiaceae.
Lygodiaceae has one genus, Lygodium, with 25-30 species four of which are found in Australia.

L. microphyllum is an invasive fern with fronds that scramble and twine up vegetation or, in open
    areas twine around themselves to form dense masses.
The branching underground rhizome is wiry, densely covered in dark brown hairs and has fibrous roots.

Fronds can be up to 30 m long with a thin, flexible midrib.
The midribs have one side flattened with ridges at the sides and can be smooth or slightly hairy.

A simplified descripton of the branching is to say that the fronds are bipinnately divided.
Widely separated, opposite pairs of leaflets branch off the frond midrib.
They are up to 20 cm long and on short stalks that are all of equal length along the frond.

Each of these leaflets then divides into 4 to 11 alternately arranged ultimate segments or pinnules.
These are pale green, up to 5 cm long and on short stalks which remain when the pinnules fall off.
Their shape varies from almost circular to ovate to triangular and they have a minutely toothed edge.

Fertile leaflets are usually smaller with semi-circular or triangular pinnules up to about 1.4 cm long.
Their edges have narrow lobes up to about 8 mm long that carry the sporangia.
Individual sporangia, on short stalks, are in cup-like flaps that open towards the tip of the lobe.