Acrostichum aureum, the golden leather fern, is a large
understory fern that occurs in mangrove forests and other wetlands.
Plants measure approximately 1.2 - 1.8m (4 - 6 feet) in height and
are as broad as they are tall. Fronds are usually arching
around the periphery of the plant, but tend to be more erect near
the center. The thick, leathery leaves are compound and large,
measuring over 1m (3.3 feet) in length, and 12 - 50 cm (4.8 - 19.7
inches) in width. There are 24 - 30 pairs of alternate leaflets
(pinnae) that are non-overlapping, rounded at the tips, and measure
approximately 10 - 34 cm (3.9 - 13.3 inches) in length X 1.3 - 7
cm (0.5 - 2.8 inches) in width. Leaves are shiny and typically
dark green above, but paler on the leaf underside. Leaf margins
are somewhat uneven and wavy in appearance.
No sori are present as in other ferns.
Rather, sporangia are distributed over the entire underside of reproductive
pinnae (the most distal 5 or more pairs), lending a felt-like texture
to these leaves. Sporangia are brick red to rust red in color,
with spores measuring 37 - 72 µm in diameter.
A related species, the giant leather fern, Acrostichum danaefolium,
is similar in appearance, but grows larger, with fronds generally
2m (6.6 feet) or more in length and pinnae set closer together.
A more definitive characteristic is the presence of reproductive
pinnae on fronds. In A. aureum, reproductive pinnae
are found only distally, whereas in A. danaefolium, pinnae
are reproductive throughout the frond (Lloyd and Greg 1975).
II. HABITAT AND DISTRIBUTION
Acrostichum aureum occurs in tropical and subtropical areas
worldwide. In the continental United States, it is restricted
to wetland areas in south and southwestern Florida.
Not present in most IRL Counties. It is present but not common
in Martin county.
III. LIFE HISTORY AND
Age, Size, Lifespan:
Plants measure approximately
1.2 - 1.8m (4 - 6 feet) in height and are as broad as they are tall.
Leaves measure approximately
1m (3.3 feet) in length, and 12 - 50 cm (4.8 - 19.7 inches) in width.
Pinnae measure approximately 10 - 34 cm (3.9 - 13.3 inches) in length
X 1.3 - 7 cm (0.5 - 2.8 inches) in width. The growth
rate is moderate (Medina et al. 1990).
Though Acrostichum aureum is abundant
in some areas of the World, in the Continental U.S. it is confined
to Southern Florida, where it is listed as a Threatened species.
Unlike other fern species, Acrostichum species do not form
sori on their reproductive leaves. Rather, sporangia are distributed
over the entire abaxal surface of reproductive pinnae, lending them
a felt-like texture. Additionally, not all pinnae on a frond
are reproductive. in A. aureum, only 5 -8 pairs of
pinnae at the tip of a frond are reproductive. This feature
helps distinguish A. aureum from another Florida congener,
the giant leather fern, A. danaefolium.
Spore germination in the golden leather
fern tends to be higher in non-saline substrates (Lloyd and Buckley
IV. PHYSICAL TOLERANCES
Acrostichum aureum is halophytic, but generally requires
fresh water for it to become established and grow optimally.
It does not grow in areas where soil salinity exceeds 50 ppt, nor
does it grow on arid coastlines (Medina 1990).
Salinity is the primary environmental stressor
and regulator of plant development in mangrove forests (Medina et
al. 1990). High salinity levels induce changes in plant height,
leaf size, and the osmotic pressure of leaf cell sap. Several
authors (Tomlinson 1956; Walter 1973) reported that A. aureum
grows optimally on somewhat elevated grounds in mangrove forests
that are well protected from frequent tidal influx and have high
rainfall, which tends to desalinate upper soil layers.
In Malaysia, 2 growth forms are recognized.
A large form grows to 4m (13.1 feet) in height and is generally
confined to the margins of mangrove forests, where it is frequently
inundated with freshwater from heavy rainfall. The other form
is stunted, growing less than 1m (3.3 feet) in height and inhabiting
areas where tides inundate the soil 10 - 28 times per month
(Medina et al. 1990).
The golden leather fern grows well in nearly all light conditions,
from full sun to dense shade (Medina et al. 1990). Maximum
rates of productivity, development, and reproductive capacity are
observed under full sun exposure; however, Acrostichum
aureum is highly shade-tolerant and takes advantage of decreased
evaporative rates in shade to reduce salt stress in estuarine environments
(Medina et al. 1990).
V. COMMUNITY ECOLOGY
Golden leather ferns inhabit neotropical mangrove swamps, salt marshes,
low hammocks, and canal margins. In many parts of the World,
they have been considered a vegetative pest that interferes with
growth and regeneration of mangrove trees (Medina et al. 1990).
However, Chan et al. (1987) showed that Rhizophora mucronata
in Malaysia could be regenerated in densely vegetated Acrostichum
The 3 species of Acrostichum all grow in loose association
with mangrove vegetation in the tropics (Tomlinson 1986).
VI. SPECIAL STATUS
The golden leather fern is listed as an Threatened species in Florida.
It is not listed at the Federal level.
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K. Hill, Smithsonian Marine Station
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