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• True ferns and moonworts
• Onoclea sensibilis

Onoclea sensibilis — sensitive fern

Facts

The susceptibility to frost of the sterile fronds gives sensitive fern its name. It spreads rapidly and can form large colonies. The spores are not released until the spring following the season in which the fertile fronds are produced.

Habitat

Meadows and fields, shores of rivers or lakes, swamps, wetland margins (edges of wetlands)

Characteristics

• Growth form

  Life form

  the plant is herbaceous and terrestrial

  Life stage

  the plant is visible as a typical leaf-bearing fern (sporophyte)

  Spore-bearing leaflets

  the spore-bearing fronds are dramatically different from the sterile fronds

• Leaves

  Features of leaves

  there are no special features on the leaves

  Leaf blade length

  13–34 cm

  Leaf blade shape

  the leaf blades are roughly triangular

  Leaf blade width

  At least 15 cm

  Leaf divisions

  • the leaf blade is compound (divided into leaflets)
  • the leaf blade is lobed

  Leaf lifespan

  the leaves drop off in winter

  Leaf stalk color

  red or red-brown to purple or black

  Leaf stalk hairs

  there are no hairs on the leaf stalk

  Leaf stalk length

  220–580 mm

  Leaf stalk relative length

  the leaf stalk is more than three quarters as long as the blade

  Leaf stalk scale location

  • the scales are present on both the lower and upper halves of the leaf stalk
  • the scales are present only on the lower half of the leaf stalk

  Leaf stalk scales

  the leaf stalk has scales

  Leaf stalk vessels

  2 bundles

  Leaf vein branching

  the secondary veins of the leaf blade split and rejoin to form a netlike pattern

  Leaf vein tips

  the veins go all the way to the edge of the leaf blade

  Leaflet relative size

  the bottom leaflets are about half as long as, to slightly longer than, the leaflets from the middle of the frond

  Leaflet stalks

  • the leaflets are stalked
  • the leaflets do not have stalks

  Lobe or leaflet length

  25–180 mm

  Lobe or leaflet pairs

  5–11

  Lobe or leaflet shape

  the lobe or leaflet is widest below the middle and tapering at both ends; lance-shaped

  Lobe or leaflet width

  15–50 mm

  Plant growth form

  the leaves grow from a rhizome growing at or below the ground

  final leaf segment margin

  the topmost lobe or leaflet of the leaf blade has a smooth or lobed edge

• Place

  Habitat

  • terrestrial
  • wetlands

  New England state

  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Rhode Island
  • Vermont

  Specific habitat

  • edges of wetlands
  • meadows or fields
  • shores of rivers or lakes
  • swamps

• Spores or spore cones

  Sorus features

  there are no special features on the sorus

  Sorus shape

  there are no sori, or they are concealed in leaf segments or hardened, capsule-like structures derived from a modified leaflet

  Sporangia location

  the spores are hidden inside hardened, rolled-under leaf segments

  Sporangium type

  the sporangia are opaque without an annulus and usually without a stalk (leptosporangiate)

  Spore forms

  there is only one type of spore present

Wetland status

Usually occurs in wetlands, but occasionally in non-wetlands. (Wetland indicator code: FACW)

New England distribution and conservation status

From the dichotomous key of Flora Novae Angliae