Identifying Southwest Florida's Ferns

Aquatic & Floating Fronds

To identify a floating/aquatic fern, begin with the first question and continue until you get a "yes" answer.

1. Are the fronds round, fingertip-sized, hairy, and in loose floating mats? YES, or 1. Are the fronds irregulary branched like a flattened juniper twig (float)? YES, or 1. Are the fronds long and antler-like, and are the stems almost "spongy" in appearance (rooted)? YES, or 1. Are the fronds large (5 to 10 inches), upright, and with strongly lobed leaves (rooted)? YES, or 1. Is the frond shaped like a 4-leaf clover and rooted in mud (usually in standing rather than moving water)? YES There are no more aquatic/floating frond questions. If it is an aquatic/floating frond , the answer to one of the above five questions will be a "yes."

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Salvinia minima

(Salvinia, Water Spangles)

floating frond

Description	round or oval, undivided, paired and opposite, 1/4-1/2" long; upper leaf surface clothed with stiff branched hairs which trap air and help plant stay upright (will flip back over when dropped in water upside-down)
Rhizome	floating on water surface or creeping on mud during dry-downs
Spores	many fine "hairs" attached to the underside of the pair of leaves are actually a third submerged leaf bearing round sporocarps; spores released underwater from this third leaf
Veins	not really
Growth	floating ferns; common where it's too shady for water lettuce ot occur
Similar	sometimes misidentified as Duckweed, whose leaves are only 1/3 as large, shaped more like grains of rice, and float individually

Azolla caroliniana

(Azolla, Mosquito Fern)

floating frond

Description	leaves minute (less than 1/2" long); smooth; branch in equal forkings along rhizome; borne in two rows; each leaf has two round lobes, the upper one green and the lower one colorless; delicate, lacy appearance; in cooler weather, has reddish cast
Rhizome	hair-like, branched; roots thread-like
Spores	sporangia produced in separate round structures (sporocarps) located in leaf axils
Veins	not really
Growth	floating fern; open water, often with Salvinia
Similar	none

Ceratopteris thalictroides (exotic)

(Water Horn Fern, Water Sprite)

floating frond

Description	an aquatic fern with a rooted stem (petiole) which is green, longitudinally ridged and furrowed, and spongy in appearance (photo above right); numerous erect fronds to 3 feet or more in length; fertile fronds are narrow, linear; sterile fronds are more leaf-like; fertile blades deeply bi- to tri- to quadri-pinnate-pinnatifid and deeply lobed (photo above left)
Rhizome	thick mass of roots under the surface of the water, frequently anchored in tussocks and mud
Spores	one to three rows on the lower surface of the fertile fronds; often enclosed by the strongly "rolled" leaf margins
Veins	not visible
Growth	aquatic to semiaquatic in slow-moving rivers, ponds, and other slow-moving water
Similar	Floating Water Fern (Ceratopteris pteridoides) whose fronds are shorter (to 50 cm) and whose petiole is mostly more than 10mm wide
Notes	a short-lived aquatic or semi-aquatic species

Ceratopteris pteridoides (rare)

(Floating Water Fern, Floating Antler Fern)

aquatic/floating frond

Description	typically floating-leaved to sometimes rooted; fronds deltate to triangular in overall outline; fertile fronds with linear segments; sterile fronds shorter and wider, more leaf-like; stem (petiole) longitudinally ridged and furrowed and spongy-looking
Rhizome	thick mass of roots under the surface of the water, frequently anchored in mud and/or tussocks
Spores	borne in crowded rows about halfway between midvein and margins; leaf edges strongly inrolled, almost encasing the sori
Veins	not noticeable
Growth	aquatic or semiaquatic in ponds and slow-moving rivers; usually floating but sometimes anchored in mud
Similar	Water Horn Fern (Ceratopteris thalictroides) has narrower petioles (stems) less than 10 mm wide and fronds are longer
Notes	a short-lived aquatic or semi-aquatic species

Marsilea vestita (rare)

(Water Clover)

aquatic/floating frond

Description	slender stems; clustered fronds; frond divided into four spreading segments giving the appearance of a large four-leaf clover, circular overall in outline
Rhizome	rise at leaf nodes
Spores	found in hairy sporocarp (beanlike structure about the size of a peppercorn that contains the sori) that grows from the roots on a very short stalk
Veins	not noticeable, but radiate out from point where four segments separate
Growth	aquatic, sometimes floating fern although it can also be found in moist roadside ditches and moist to dry soil of lawns and flower beds
Similar	none in South Florida