Penthorum

Scientific name

Penthorum L.

Common names

ditch stone crop, Virginia stone crop

Family

Penthoraceae

Similar genera

Bidens, Eclipta, Epilobium, Hygrophila, Limnophila aromatica, Ruellia, Shinnersia

Native distribution

North America, Asia, and far eastern Russia

Species cultivated

Penthorum sedoides L. is sometimes commercially available as a pond and aquarium plant

Penthorum chinense Pursh

Adventive distribution

information not available

Weed status

not weedy

Habit

semi-aquatic herb

Brief description

Rhizomatous; stems ascending to erect, simple or ± branched, ± angled, glabrousglabrous:
(adj) without hairs or scales
basally, stipitate-glandular hairs above. Leaves alternatealternate:
(adj) (of leaves) bearing one leaf per node; placed singly on the stem at different heights
; sessilesessile:
(adj) attached directly, without a stalk
or shortly 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)
lanceolate to ellipticelliptic:
(adj) in the form of an ellipse (oval)
, glabrousglabrous:
(adj) without hairs or scales
or sparsely haired below; apexapex:
(n) the point farthest from the point of attachment; the tip (often pointed)
acuminateacuminate:
(adj) tapering gradually to a point and forming more or less concave sides
; base narrowly cuneatecuneate:
(adj) wedge-shaped; triangular, with narrow end at the base
; marginmargin:
(n) edge; rim
serrate; venationvenation:
(n) the arrangement of veins in a leaf
pinnatepinnate:
(adj) in the form of a feather; of, e.g., leaflets, lobes, or veins: arranged in two rows along an axis
. Inflorescenceinflorescence:
(n) the arrangement of flowers on the floral axis
a terminalterminal:
(adj) at the apex
or axillaryaxillary:
(adj) in, of, or produced from an axil
helicoid cymecyme:
(n) a determinate, usually flat-topped or convex inflorescence in which the terminal flower blooms earliest
, pedunculatepedunculate:
(adj) borne on or possessing a peduncle
; bracts ovateovate:
(adj) egg-shaped in outline; generally with the broad end at or near the base
, small; pedicelspedicels:
(n) the stalk of a single flower in an inflorescence, or of a grass spikelet
glandular. Flowers small, yellow-green, white; sepals 5, triangular, margins entireentire:
(adj) having a continuous margin that is not toothed or lobed
or serrulateserrulate:
(adj) minutely serrate
; petals typically absent or 5, lanceolatelanceolate:
(adj) lance-shaped; widest point below the middle, tapering to the apex
, slightly clawed; stamens 10 in 2 whorls; carpels 5, united below, styles short, forming beaks in fruit, stigmasstigmas:
(n) the portion of the pistil that is receptive to pollen
small, capitatecapitate:
(adj) terminated by an enlarged and rounded head
.

Natural habitat

margins of streams and rivers, in ditches, marshes, swamps and floodplains

Additional comments

A small genus of two species; of the two, Penthorum chinense has narrower leaves, more robust styles, and fewer-flowered inflorescences than P. sedoides.

Limnophila aromatica (=L. aromaticoides) is frequently missidentified as Penthorum sedoides. Penthorum does not grow strongly submersedsubmersed:
see submerged
, (unlike L. aromatica) and is not as common in the hobby as L. aromatica.