Nomenclature

Species name:

Polygonum maritimum   L.

Author(s):

Carl von Linné
   Sweden, 1707-1778

General names:

Sea Knotgrass

Maltese name:

Lewża tal-baħar

Plant Family:

Polygonaceae   (Dock Family)

Name Derivation:

Polygonum = Derived from the Greek words polys, "many," and gonu, "knee or joint," hence "many joints" because of the numerous thickened joints on the stem. (Greek);
Maritimum = Maritime, related to coast or sea (Latin).

Synonyms:

Polygonum glaucum, P.littorale, P. parviflorum

Plant Description

Life Cycle:

Perennial

Habitat:

On sandy shores.

Source in Malta:

Very rare in Malta, seen on sandy bays of St. Maria in Comino and of Ramla tat-Torri in Malta.

Plant Height:

May reach up to 50cm in height.

Flowering Time:

Apr - Jul

The Sea Knotgrass is a perennial plant that grows usually in sand dunes on most of the European shores. Like other members of the genus Polygonum it grows crawling, growing slowly upwards up to 50cm in height. However, being a perennial it has a stouter, woodier and hairless stem than the other species of the same genus that live in our islands.

The Leaves grow alternately on the branched stems. The Stipules are united in a membranous sheath called the Ochrea. This is a characteristic of the Family Polygonaceae. In this species the Ochrae is reddish-brown at the base where it is attached to the stalk, from which vertically dark-coloured veins come up. The upper part of the Ochrae is silver in colour and typically membrane-like. The leaves are usually elliptical in shape (an elongated oval shape) and may reach up to 2cm in length. They end in a point and are bluish-green (glaucous) in colour.

The Perianth (flower + sepals) is very small reaching up to 5mm in size. The flowers are hermaphrodite and have tiny pink or white petals. The flowers usually develop singly along the branches, but occassionally grow into small groups of up to 4 along the stem. There are 5 petals and sepals - the sepals are smaller than the flowers. Bracts are tiny and leaf-like. There are usually 8 stamens and 2-3 stigmas in each flower.

The nut is up to 5mm and just exceeds the perianth in size. It has 3 angles (trigonous) and lacks wings. Besides the fruit can float over the water, and can colonise beaches further away from the main poulation.

The presence of Ochrae identify this species as belonging to the Polygonaceae family. The fact that the species has flowers that grow singly or in small groups and the ochrae is silvery on the distal part identify it from members of the genera Persicaria and Fallopia. The lack of spines on the fruit excludes the genera Rumex and Emex. It differs from other members of the same genus because it is perennial with a woody stock, and flowers are in single groups.

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