Trapa

Scientific name

Trapa L.

Common names

European water chestnut, horn chestnut, saligot, jesuit nut, water caltrope

Family

Lythraceae

Similar genera

Ludwigia (rarely confused)

Native distribution

Eurasia, northern Africa

Species cultivated

Trapa natans L. (with numerous geographical varieties)

Adventive distribution

northeastern United States, Canada

Weed status

The high weed potential of this plant is widely accepted. Trapa is a noxious weed and a prohibited import in many countries.

Habit

attached stem plantstem plant:
(n) (a term used in the aquarium and pond plant trade) having an elongate stem (as opposed to a compact stem)
with apicalapical:
(adj) of the apex
, floating rosetterosette:
(n) a radiating cluster of leaves, usually close to the ground at the base of a plant

Brief description

Annual. Stem attached to substrate, submersedsubmersed:
see submerged
, elongate, relatively unbranched. Leaves dimorphic: submersedsubmersed:
see submerged
leaves oppositeopposite:
(adj) (of leaves) two leaves per node; in pairs on opposite sides of an axis
, sessilesessile:
(adj) attached directly, without a stalk
, linear; floating and emergentemergent:
(adj) (syn. emersed) with parts raised out of the water; extending up out of the water
leaves alternatealternate:
(adj) (of leaves) bearing one leaf per node; placed singly on the stem at different heights
in apicalapical:
(adj) of the apex
rosetterosette:
(n) a radiating cluster of leaves, usually close to the ground at the base of a plant
, petiolepetiole:
(n) the stalk of a leaf
often swollen with spongy aerenchymaaerenchyma:
(n) plant tissue with large, gas-filled intercellular spaces that facilitates gaseous exchange and maintains buoyancy
, leaf bladeblade:
(n) (syn. lamina) the flat, expanded part of a leaf, frond, or petal (excluding, e.g., the petiole)
rhombic, venationvenation:
(n) the arrangement of veins in a leaf
pinnate, marginmargin:
(n) edge; rim
serrateserrate:
(adj) (of a leaf margin) bearing sharp teeth pointing forward or to the apex
. Submersedsubmersed:
see submerged
linear leaves, once abscised, are replaced with green pinnately-branched adventitiousadventitious:
(adj) of an organ growing where it is not normally expected, e.g., roots growing from a stem
roots that develop from leaf scar. Inflorescenceinflorescence:
(n) the arrangement of flowers on the floral axis
a solitary, bisexualbisexual:
(adj) having both male and female sexual reproductive structures on one individual or in one flower
flower, borne on short axillaryaxillary:
(adj) in, of, or produced from an axil
pedicelpedicel:
(n) the stalk of a single flower in an inflorescence, or of a grass spikelet
. Sepals 4, these developing into 2 to 4 distinctive, but highly polymorphicpolymorphic:
(adj) displaying multiple forms (of, e.g., an organ) in one organism
spines on fruit; petals 4, white to purple. Dispersal by seed.

Natural habitat

still waters of lakes, ponds, and upper regions of estuaries

Additional comments

The common name water chestnut is also applied to Eleocharis dulcus (Burm.) Hensch. and can lead to some confusion. Both species have edible seeds or tubers. Trapa natans is considered threatened in some regions of its native distribution (e.g. Germany, Belgium, Holland, and Sweden) but is a troublesome weed in much of its adventiveadventive:
(adj) introduced, non-native, or added; introduced and naturalized
distribution. The variability of this species, especially regarding seed shape, has led to multiple species being recognised across its broad distribution. The genus was recently transfered to the family Lythraceae from Trapaceae.