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horn-leaf riverweed, podostémon à feuilles cornées, threadfoot

Roots

flattened or elliptic, 0.3–1.1 mm diam.

Stems

1.8–9 mm apart, 0.4–300 × 0.5–1.5 mm at base.

Leaves

stipules caducous (absent from leaves 3–9 nodes back from stem apex), 0.5–3.6 mm, margins entire;

petiole arising perpendicular to stem axis or upright, 0.4–59 mm;

blade 1–13 times dichotomously divided, 1.7–142 mm, ultimate divisions flattened, spatulate, linear, or awl-shaped, 0.2–40 × 0.05–0.8 mm, central vein faint or absent.

Inflorescences

spathella 1.5–6.2 × 0.8–1.8 mm.

Pedicels

0.4–2.9 mm, to 0.6–10.5 mm in anthesis, 0.5–9 mm in fruit.

Flowers

tepals linear or awl-shaped, apex acute, lateral tepals 0.7–2 mm, andropodial tepals 0.1–1.1 mm;

andropodium 0.1–3.3 mm, 0.7–4.3 mm in anthesis;

filaments 0.2–0.9 mm, 0.3–2 mm in anthesis;

anthers 0.5–1.5 × 0.4–0.8 mm;

ovary 0.7–2.6 × 0.4–1.4 mm;

stigmas 0.3–1.4 mm, 0.4–1.5 mm in anthesis.

Capsules

1.4–3.1 × 0.7–1.7 mm.

Seeds

0.4–0.8 × 0.5–0.8 mm.

Podostemum ceratophyllum

Phenology Flowering Jun–Sep.
Habitat Attached to rocks and other solid substrata in swift currents
Elevation 0–800 m (0–2600 ft)
Distribution
from FNA
AL; AR; CT; GA; KY; LA; MA; MD; ME; MS; NC; NH; NJ; NY; OH; OK; PA; RI; SC; TN; VA; VT; WV; NB; NS; ON; PE; QC; West Indies (Dominican Republic); Central America (Honduras)
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Discussion

Podostemum ceratophyllum is listed as rare, endangered, or of special concern in some regions. Paucity of appropriate habitat and human disturbances (for example, siltation, damming) have contributed to conservation concerns.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Source FNA vol. 6, p. 70.
Parent taxa Podostemaceae > Podostemum
Synonyms Lacis ceratophylla, P. abrotanoides, P. ceratophyllum var. abrotanoides, P. ceratophyllum var. circumvallatum, P. ceratophyllum var. fluitans
Name authority Michaux: Fl. Bor.-Amer. 2: 165, plate 44. (1803)
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