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Isoetes lacustris — lake quillwort

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New England distribution

Adapted from BONAP data

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North America distribution

Adapted from BONAP data

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Facts

Lake quillwort grows, often completely submerged, in cold clear water of lakes and slow-moving streams, sometimes more than 10 feet (3 meters) below the water's surface.

Habitat

Lacustrine (in lakes or ponds), riverine (in rivers or streams)

Characteristics

Habitat
aquatic
New England state
  • Connecticut
  • Maine
  • Massachusetts
  • New Hampshire
  • Vermont
Leaf shape
the vegetative leaves are long and narrow
Spore leaf arrangement
the sporophylls are located in a whorl at the base of the plant
Form of shoot
NA
Horizontal stem
NA
Leaf differences
the vegetative leaves within a node are all similar in size and shape
Teeth on leaf edges
the edges of the vegetative leaves have no teeth
Constriction zones
  • NA
  • NA
Spore leaf length
Up to 250 mm
Leaf outline
the vegetative leaves are long and very narrow (linear)
Show all characteristics

  • Clonal plantlets

    Gemma arrangement
    NA
    Gemma shape
    NA
    Gemma width
    0 mm

  • Leaves

    Leaf differences
    the vegetative leaves within a node are all similar in size and shape
    Leaf length
    Up to 250 mm
    Leaf orientation
    • the vegetative leaves curve outwards and downwards from the main stem
    • the vegetative leaves spread away from the stem
    • the vegetative leaves spread slightly away from the stem, at a steep angle
    Leaf outline
    the vegetative leaves are long and very narrow (linear)
    Leaf ranks
    NA
    Leaf shape
    the vegetative leaves are long and narrow
    Spore leaf length
    Up to 250 mm
    Teeth on leaf edges
    the edges of the vegetative leaves have no teeth

  • Place

    Habitat
    aquatic
    New England state
    • Connecticut
    • Maine
    • Massachusetts
    • New Hampshire
    • Vermont
    Specific habitat
    • in lakes or ponds
    • in rivers or streams

  • Spores or spore cones

    Cone base at stem
    NA
    Cone stalk branching
    NA
    Cone thickness
    0 mm
    Cone width
    0 mm
    Length of cone
    0 mm
    Number of cones
    0
    Quillwort itssue covering spores
    the velum covers less than half of the spores
    Same or different spores
    there are two different types of spores present
    Spore diameter
    0.0549–0.75
    Spore girdle
    there is a papillose girdle alongside the equatorial ridge
    Spore leaf arrangement
    the sporophylls are located in a whorl at the base of the plant
    Spore leaf lifespan
    the sporophylls remain green for the life of the plant
    Spore leaf orientation
    the sporophylls slant upwards at a steep angle
    Spore leaf shape
    the spore-bearing leaves are long and narrow
    Spore leaf teeth
    The edges of the spore-bearing leaves are smooth, and without teeth
    Spore texture
    the spore surface is crested with a narrow irregular ridge (cristate)
    Sporophyll ranks
    NA
    Sterile tip of cone
    NA

  • Stem, shoot, branch

    Branch cross-section
    NA
    Branch form
    NA
    Constriction zones
    • NA
    • NA
    Form of shoot
    NA
    Horizontal stem
    NA
    Horizontal stem length
    0 mm
    Horizontal stem thickness
    0 mm
    Stem height
    0 mm

Wetland status

Occurs only in wetlands. (Wetland indicator code: OBL)

New England distribution and conservation status

Distribution

Connecticut
present
Maine
present
Massachusetts
present
New Hampshire
present
Rhode Island
absent
Vermont
present

Conservation status

Exact status definitions can vary from state to state. For details, please check with your state.

Connecticut
unrankable (S-rank: SU)
Massachusetts
extremely rare (S-rank: S1), endangered (code: E)
New Hampshire
historical (S-rank: SH), endangered (code: E)
Vermont
extremely rare (S-rank: S1)

Native to North America?

Yes

Sometimes confused with

Isoetes hieroglyphica:
megaspores with a smooth girdle, reticulate with low, rounded ridges (vs. I. lacustris, with megaspores with a papillate girdle, cristate to reticulate with sharp or roughened crests).
Isoetes tuckermanii:
with very similar megaspores but smaller (0.4-0.65 mm in diameter) and commonly growing in water shallower than 1 m (vs. I. lacustris, with megaspores larger, 0.55-0.75 mm in diameter) and commonly growing in water 1 m or deeper).

Synonyms

  • Isoetes macrospora Durieu

Family

Isoetaceae

Genus

Isoetes

Help

From the dichotomous key of Flora Novae Angliae

5.  Isoetes lacustris L. N

lake quillwort. Isoetes macrospora Durieu • CT, MA, ME, NH, VT; also reported from RI by Taylor et al. (1993), but specimens are unknown. Cold, clear water of lakes and slow-moving streams, sometimes at depths greater than 3 m. North American plants have been segregated from Old World plants as Isoetes macrospora. However, there does not appear to be any basis for separation other than geography. Therefore, I. macrospora is not recognized here as a distinct taxon.

5×8. Isoetes lacustris × Isoetes tuckermanii → Isoetes ×‌harveyi A.A. Eat. is known only from ME within New England. Given that its two parents are very similar in megaspore ornamentation (though the spores differ 
in size), this hybrid is recognized by possession of megaspore texture similar to that 
of I. lacustris or I. tuckermanii, but with many polymorphic spores (as in all quillwort hybrids) and the well-formed ones 0.52–0.64 mm in diameter.