Terrestrial ferns, sometimes growing in swamps; rhizome erect or creeping, solenostelic or dictyostelic, clothed with scales. Fronds long-stipitate, with a +/- U-shaped vascular strand, the lamina pinnatifid to 2 - 3-pinnate, sometimes tripartite with the basal pinnae greatly enlarged, +/- glabrous, the venation free to regularly anastomosing, the free veins terminating at the margin. The sori elongate along the margin and protected by a scariose reflected pseudoindusium attached to the margin and opening inwards, or exindusiate and completely covering the lower surface of the lamina or a large part of it; annulus longitudinal interrupted; spores trilete, rarely monolete.
A family widespread in the tropical and warmer temperate areas of the world, considered here in the narrow sense, with 5 genera containing c. 3000 species. In Papuasia there are 2 genera with c. 27 species; Acrostichum is the only aquatic genus.
Erect terestrial or subaquatic ferns of medium to large size, mostly in brackish, sometimes freshwater, swamps and marshes. Rhizome woody, short, stout, erect, dictyostelic with meduallary strands, bearing broad thick scales attached by a broad base, often with aerenchymatous strut-roots. Fronds long stipate, the stipes adaxially grooved, with a single U-shaped vascular strand, the lamina simply pinnate, the pinnae alternate, stalked, large, lanceolate or narrow-oblong, entire, thick-coriaceous, the apical pinnae similar to the lateral, a few reduced glandular pinnae that function in young fronds represented by short residual spines on the stipe, costa prominent, no main veins evident, venation oblique, cloely anastomosing to form many series of irregular but +/- uniform, narrow areoles, without included free veinlets. Sporangia acrostichoid, densely covering all or the apical half of the abaxial surface of the apical few pinnae, the fertile portions slightly contracted; exindusiate, parphyses numerous, apically clavate or variously lobed (? = abortive sporangia), annulus longitudinal, interrupted, of 20 - 22 thickened cells. Spores trilete, pale, minutely tuberculate.
Distribution: A genus of 2 species, both of which are present in Papuasia. However, only Acrostichum aureum occurs in strictly fresh water habitats, as Acrostichum speciosum requires a more or less brackish environment.
Croft, J.R. 1985. Ferns and Fern Allies, in Leach, G.J. & Osborne, P.L. 1985. Freshwater Plants of Papua New Guinea. 33 - 74, f. 6 - 13, pl. 5 - 7.
Holttum, R.E. 1954 (revised 1965). Ferns of Malaya. A revised flora of Malaya. Volume 2. 1 - 643. Govt. Printer, Singapore.
Two species in Papuasia:
|1||Apex of sterile pinnae abruptly rounded or truncate and shortly tipped; young fronds strap-like...||A. aureum|
|Apex of sterile pinnae narrowly acuminate; young fronts broadly lanceolate...||A. speciosum|
Caudex stout and erect to 5 x 10 cm, bearing polished, dark brown scales to 1 x 3 cm, and many narrower smaller scales, spreading onto the stipe bases. Frond to 2 m or more tall, stipe to 80 cm long, 1 - 1.5 cm diameter, pinnae on stalks to 2 cm long, oblong, to 3 - 7 x 20 - 40 cm, apex abruptly rounded to truncate, or retuse, shortly mucronate, base asymmetric, rounded to cuneate, margin entire, coriaceous, glabrous, midrib groved above, strongly prominent below, veins with areoles roughly elongated at 50 - 70 degrees to the midrib, apical pinna similar to lateral pinnae, sessile and often slightly decurrent; when fertile the apical few pinnae slightly contracted, completely covered with sporangia beneath, sometimes only the apical half of a pinnae fertile, sporangia mixed with paraphyses with many-lobed apical cells.
Habitat: In brackish conditions, within and behind mangrove swamps, rooted in the mud below high tide level, often as large clumps on mounds, sometimes forming large stands. Also in inland freshwater swamps and marshes, around lake margins, at low altitudes.
Distribution: A pantropic species known from most humid tropical areas of the world, especially those with mangrove formations. In Papuasia not as widespread as the following species, most specimens of which were assigned to Acrostichum aureum in the past.
Notes: See note under Acrostichum speciosum
Caudex stout and erect to 5 x 10 cm, bearing polished, dark brown scales to 5 x 10 cm, spreading onto the stipe bases. Frond to 30 - 150 cm tall but mostly less than 1 m, stipe to 50 cm long, 3 - 8 mm diameter, pinnae on stalks to 1 cm long, lanceolate to oblong-lanceolate, to 2 - 4 x 10 -20 cm, apex attenuate or acute or acuminate, base asymmetric, cuneate to rounded cuneate, margin entire, coriaceous, glabrous, midrib grooved above, strongly prominent below, veins with areoles roughly elongated at 50 - 70 degrees to the midrib, apical pinna similar to lateral pinnae, sessile and often slightly decurrent; when fertile the apical few pinnae slightly contracted, completely covered with sporangia beneath, sometimes only the apical half of a pinnae fertile, sporangia mixed with paraphyses with many-lobed apical cells.
Habitat: Similar to Acrostichum aureum, but tending to prefer more exposed mangrove situations, or in limestone crevices along coral coasts. Generally abesent from inland freshwater situations.
Distribution: This species is restricted to tropical and southeast Asia and northern Australia. In Papuasia it has been collected from most coastal regions. It is more often collected than Acrostichum aureum.
Notes: The two species of Acrostichum are very closely related and are sometimes difficult to separate, especially in the absence of a range of adequate material. In the past all specimens were included under Acrostichum aureum, but generally speaking it is possible to assign specimens to on or other of the species with very little uncertainty.