Helanthium

Scientific name

Helanthium (Benth. & Hook.f.) Engelm. ex J.G.Sm.

Common names

sword plant, chain sword

Family

Alismataceae

Similar genera

Sagittaria graminea

Native distribution

North and South America

Species cultivated

(two species [often sold under Echinodorus synonyms] plus cultivated varieties); available through hobbyists and frequently commercially

Helanthium bolivianum (Rusby) Lehtonen & Myllys

H. tenellum (Mart. ex Schult.f.) J.G.Sm.

Adventive distribution

none

Weed status

not weedy

Habit

aquatic or semiaquatic, emergentemergent:
(adj) (syn. emersed) with parts raised out of the water; extending up out of the water
or submergedsubmerged:
(adj) (syn. submersed) under water; submerged below the water surface
herb; produces numerous stolons to form chain-like networks of plants.

Brief description

Small, highly stoloniferous. Stem a compact basalbasal:
(adj) at or pertaining to the base, or point of attachment
rosetterosette:
(n) a radiating cluster of leaves, usually close to the ground at the base of a plant
. Leaves basalbasal:
(adj) at or pertaining to the base, or point of attachment
, erect, ascending or floating; emersedemersed:
see emergent
leaves petiolatepetiolate:
(adj) relating to or in the form of a petiole; bearing petioles
, leaf bladeblade:
(n) (syn. lamina) the flat, expanded part of a leaf, frond, or petal (excluding, e.g., the petiole)
linear to ellipticelliptical:
(adj) in the form of an ellipse (oval)
, apexapex:
(n) the point farthest from the point of attachment; the tip (often pointed)
acute to acuminateacuminate:
(adj) tapering gradually to a point and forming more or less concave sides
, base attenuateattenuate:
(adj) narrowing gradually to a point
, margins entireentire:
(adj) having a continuous margin that is not toothed or lobed
; submersedsubmersed:
see submerged
leaves are sessilesessile:
(adj) attached directly, without a stalk
leaf-like petioles (no true bladeblade:
(n) (syn. lamina) the flat, expanded part of a leaf, frond, or petal (excluding, e.g., the petiole)
), linear, light to dark green. Inflorescenceinflorescence:
(n) the arrangement of flowers on the floral axis
axillary, an umbelumbel:
(n) a flat to convex inflorescence in which the flower pedicels (called rays) all arise from the same point
or a racemeraceme:
(n) an indeterminate, unbranched inflorescence having pedicelled flowers on a usually elongated axis (may be cymose)
, typically of 2-3 whorls. Flowers pedicellatepedicellate:
(adj) borne on a pedicel
; bracteatebracteate:
(adj) possessing or bearing bracts
; sepals 3, erect; petals 3, clawed, larger than sepals; stamens (6-)9; carpels numerous, separate; white. Reproduces vegetatively by numerous runners.

Natural habitat

marshy locations, shores of rivers, lakes or pools, in shallow water

Additional comments

Helanthium tenellum is the smallest species of the three in the genus, and is rather variable. Helanthium species were previously in the genus Echinodorus Rich. and are still frequently sold under this genus. In a phylogentic analysis of Echinodorus, Helanthium was separated into its own genus, which is supported by both morphological and molecular analyses (Lehtonen and Myllys, 2008).