Blechnum occidentale L., Blechnaceae

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Present on Pacific Islands?  yes

Primarily a threat at high elevations?  no

Other Latin names:  Blechnum appendiculatum Willd.

Common name(s): [more details]

English: hammock fern, New World midsorus fern

Habit:  fern

Description:  var. puberulum Sodiro: "Rhizomes erect, sometimes elongate and to 12 cm long, 8-20 thick, closely invested with dark brown, lanceolate scales 4-8 mm long, their central line darker brown and more lustrous than marginal banks; stolons usually present, 1.3-2 mm thick, dark brown; stipes fasiculate, 6-16 cm long, shorter than blades, stramineous, 0.7-2.5 mm thick, glabrous but sparsely scaly on basal 2-4 cm; blades ovate to lanceolate, mostly 16-50 cm long, 5-25 cm broad, pinnate at base, pinnatisect above and gradually reduced toward the elongate, pinnatifid, more or less acuminate apex; rachis puberulous, pilosulous or glandular-pilosulous, roughened by minute conical pustules or papillae visible under high magnification; pinnae and segments horizontal or nearly so, numerous, (10) 15-40 pairs, the middle 2.5-7 cm long, 7-13 mm wide, subobtuse to acuminate, sometimes slightly apiculate, margins entire and smooth to shallowly crenulate-undulate and bearing microscopic crystalline teeth, the lower 3-10 pairs free from rachis, sessile, cordate at base, rounded-biauriculate, the upper auricle rounded, overlapping rachis, lowest pinnae slightly smaller than middle ones but not strongly reduced or minute, all subcoriaceous, light green, glabrous except sometimes immediately adjacent to rachis beneath; fertile blades essentially like sterile but with somewhat longer stipes; sori costal, extending from near base to slightly below apex of pinna, sterile band between sorus and margin half again to 3 times as wide as sporulating band; indusia thin, entire, glabrous, 0.6-1 mm wide before rupture by enlarging sporangia, then somewhat obscure; sporangia very numerous, pale rufous brown, about 0.15-0.2 mm long, half as thick; annulus of 12-16 thickened cells; spores bilateral, broadly ellipsoidal, 40-45 microns thick, 55-60 microns long, surfaces smooth to finely and sparingly ridged with minute, irregularly spaced, rounded ridges, brownish gold by transmitted light"  (Wiggins & Porter, 1971; pp. 103-105).

Wilson (1996) classifies this species in Hawai‘i as Blechnum appendiculatum which differs in having rachises that are pubescent and glandular on the abaxial surface; however, GRIN says the species are synonymous.

Habitat/ecology:  In Hawai‘i, "a very common weedy fern along trail sides, stream banks, forested slopes, and gulches on all islands, often growing in solid stands" (Wilson, 1996); "displaces low-growing plants on the forest floor"  (Motooka et al., 2003)..  "In rather open and sometimes dry situations" (Wiggins & Porter, 1971; pp. 103-105).

Propagation:  Spores

Native range:  Mexico, Central and South America, West Indies (GRIN).

Presence:

Pacific
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
State of Hawaii Hawaiian Islands	Hawai‘i (Big) Island	introduced invasive	Wilson, K. A. (1996)
State of Hawaii Hawaiian Islands	Kaho‘olawe Island	introduced invasive	Wilson, K. A. (1996)
State of Hawaii Hawaiian Islands	Kaua‘i Island	introduced invasive	Wilson, K. A. (1996)
State of Hawaii Hawaiian Islands	Lāna‘i Island	introduced invasive	Wilson, K. A. (1996)
State of Hawaii Hawaiian Islands	Maui Island	introduced invasive	Wilson, K. A. (1996)
State of Hawaii Hawaiian Islands	Moloka‘i Island	introduced invasive	Wilson, K. A. (1996)
State of Hawaii Hawaiian Islands	Ni‘ihau Island	introduced invasive	Wilson, K. A. (1996)
State of Hawaii Hawaiian Islands	O‘ahu Island	introduced invasive	Wilson, K. A. (1996)

Pacific Rim
Country/Terr./St. & Island group	Location	Cited status & Cited as invasive & Cited as cultivated & Cited as aboriginal introduction?	Reference & Comments
Australia Australia (continental)	Queensland	introduced invasive	Australian Biological Resources Study (2011) "Naturalised in rainforest margins".
Chile (continental) Chile	Chile (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Colombia Colombia	Colombia (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Costa Rica Costa Rica	Costa Rica (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Ecuador (Mainland) Ecuador	Ecuador (Republic of) (continental)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
El Salvador El Salvador	El Salvador (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Guatemala Guatemala	Guatemala (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Honduras Honduras	Honduras (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Mexico Mexico	Mexico (United Mexican States)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Nicaragua Nicaragua	Nicaragua (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Panama Panama	Panama (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)
Perú Perú	Perú (Republic of)	native	U.S. Dept. Agr., Agr. Res. Serv. (2011)

Control: 

Chemical: "Probably susceptible to dicamba and glyphosate"  (Motooka et al., 2003).

Additional information:
Excerpt from the book "Weeds of Hawaii‘s Pastures and Natural Areas; An Identification and Management Guide" (Motooka et al., 2003). (PDF format).

Additional online information about Blechnum occidentale is available from the Hawaiian Ecosystems at Risk project (HEAR).

Information about Blechnum occidentale as a weed (worldwide references) may be available from the Global Compendium of Weeds (GCW).

Taxonomic information about Blechnum occidentale may be available from the Germplasm Resources Information Network (GRIN).

References:

Australian Biological Resources Study. 2011. Flora of Australia Online. Australian Biological Resources Study, Canberra.

Motooka, Philip/Castro, Luisa/Nelson, Duane/Nagai, Guy/Ching, Lincoln. 2003. Weeds of Hawaii‘s Pastures and Natural Areas; An Identification and Management Guide. College of Tropical Agriculture and Human Resources, University of Hawaii at Manoa. 184 pp.

Rejmánek, M. 1996. Species richness and resistance to invasions. In: Orians, G., R. Dirzo and J. H. Cushman (eds.). Biodiversity and ecosystem processes in tropical forests. Springer-Verlag. pp. 153-172.

Staples, George W./Herbst, Derral/Imada, Clyde T. 2000. Survey of invasive or potentially invasive cultivated plants in Hawai‘i. Bishop Museum Occasional Papers No. 65. 35 pp.

U.S. Dept. Agr., Agr. Res. Serv. 2011. National Genetic Resources Program. Germplasm Resources Information Network (GRIN). Online searchable database.

Wiggins, I. L./Porter, D. M. 1971. Flora of the Galapágos Islands. Stanford University Press. 998 pp.

Wilson, K. A. 1996. Alien ferns in Hawai‘i. Pacific Science. 50(2):127-141.