Blechnum dilatatum

Primary tabs

Blechnum dilatatum


Asia-Tropical, E Highlands present, Milne Bay present, Papua New Guinea mainland present, S Highlands present, W Highlands present
Malesia: Papua New Guinea mainland (W Highlands, S Highlands, Milne Bay, E Highlands).


1. We have concluded that B. decorum var. dilatatum is not closely related to B. decorum Brause. Further, we have reduced this latter to a synonym of B. hieronymi. Blechnum dilatatum as here defined possesses a consistently pale stipe and rhachis and usually has much larger fronds and a much broader lamina (hence the specific epithet dilatatum) than does B. hieronymi. In B. dilatatum the wavy cartilaginous pinna margins are never revolute, and often are entire becoming serrate towards the apices. In both B. decorum (now B. hieronymi) and B. dilatatum the pinnae at the base of the lamina can be either petiolate or sessile.
2. Another species closely related to B. dilatatum, B. nesophilum, appears to replace B. dilatatum on the mountain ridges of the Admiralty Islands, New Britain and New Ireland. Blechnum dilatatum differs from B. nesophilum in a number of details; these are discussed in the notes with B. nesophilum.
3. Specimens of B. dilatatum collected from forest habitats have thinner pinnae, more spaced on the rhachis, and may appear at first sight to be distinct from plants collected from open swamp and grassland situations. Plants from the exposed habitats usually have thick leathery pinnae, often overlapping and crowded on the rhachis; fresh specimens are a brighter green on the upper lamina surface and paler green underneath.
4. Juvenile plants of B. dilatatum often have 6-10 small fronds 5-10 cm in length with 1-3 pairs of short rounded pinnae 1 cm long and the terminal pinna 2-2.5 cm in length and broadly narrowly elliptic, acuminate to attenuate. Various intermediates indicate a continuous gradient to the large mature plants. The intermediate plants, 25-40 cm in height and with 6-10 pairs of pinnae, often produce fertile fronds; the basal fertile pinnae usually have a broader sterile area adjoining the rhachis while the pinnae towards the apex may possess a small decurrent sterile zone; nearer the apex the pinnae lack the sterile zone; the terminal pinna on both the fertile and the sterile fronds is 10 or more cm long, which is twice the length of the lateral pinnae.