Tetrachondra

Tetrachondra
Scientific classification
Kingdom:	Plantae
(unranked):	Angiosperms
(unranked):	Eudicots
(unranked):	Asterids
Order:	Lamiales
Family:	Tetrachondraceae; Skottsb.
Genus:	Tetrachondra; Petrie (1892)
Species
	Tetrachondra hamiltonii; Tetrachondra patagonica;

Tetrachondra is a plant genus and the only member of the family Tetrachondraceae. It comprises two species of creeping succulent, perennial, aquatic or semi-aquatic herbaceous plants. Its distribution range is disjunct: one species is endemic to New Zealand (mainly Stewart Island, Otago and Southland) while the other one is endemic to southern Patagonia and Tierra del Fuego. These plants bear essential oils.

Description

Leaves

The leaves stem short and erect from prostrate rooting stems. They are simple, opposite leaves, with aromatic glands and no stipule. The leaves are connate by flattened petioles. The lamina is simple, minutely denticulate on the margin, and leathery on the surface.

Flower

Flowers are solitary and can be axillary or terminal. They are tetramerous, without free hypanthium. There are a distinct calyx, which consists of 4 fused sepals, and a distinct corolla, consisting of 4 fused petals.

The androecium consists of 4 free, epipetalous stamens, all of which are fertile. The stamens alternate with the corolla lobes. The anthers are dorsifixed and introrse. Pollen grains are aperturate and colporate.

The gynoecium consists of 2 carpels. Each carpel is deeply lobed, giving the impression that there are in fact 4 carpels, ostensibly isomerous with the perianth. The ovary is syncarpous and have either 4 or 2 locules, each one housing 1 or 2 anatropous ovules. Stigmas are inconspicuous. The placentation mode is basal.

Fruit and seed

The fruit is a schizocarp associated with 4, one-seeded, setulose nutlets. The seeds are extensively endospermic.

Reproduction

These plants are hermaphrodite.

Alternative and previous classification

Tetrachondra is also variously ascribed to families Lamiaceae (such as in the Cronquist's classification or the Dahlgren's classification) and Scrophulariaceae.