A16 - Callitriche Stagnalis Community

Summary

Synonymy

Swift-moderate current vegetation Butcher 1933 p.p.

Constant species

Callitriche stagnalis.

Physiognomy

All the starwort vegetation sampled has been grouped in this Callitriche stagnalis community, usually dominated by C. stagnalis, occasionally accompanied or locally replaced by C. platycarpa or, in southern Britain, C. obtusangula. Sometimes the plants grow fully submerged, though there are usually at least some shoots trailing to the water surface and, where pools or streams periodically dry out, the vegetation may persist for some time on the moist ground. Maximum growth is generally attained early in the season, but total cover is very variable: many stands are small, but dense luxuriant growth can occur in congenial situations, while just sparse shoots remain in unstable habitats. Colonisation of new sites can be very rapid and, once well established, populations can be long-lived but, in temporary water bodies or disturbed situations, like spatey streams or frequently cleared dykes, stands may be ephemeral.

This kind of vegetation is found in close association with a variety of other aquatics, but associates actually growing within thicker stands are few in number and usually of low cover. In some situations, Potamogeton pectinatus becomes a constant feature and it may occur abundantly among the Callitriche but, otherwise, there are generally just occasional shoots of Myriophyllum spicatum, M. alterniflorum and Ceratophyllum demersum, with a few thalli of Lemna minor sometimes caught among the floating shoots.

Sub-communities

Callitriche spp. sub-community. Starworts are the sole dominants here, with C. stagnalis constant and occasional C. platycarpa or C. obtusangula but no P. pectinatus.

Potamogeton pectinatus sub-community. P. pectinatus becomes constant here and it can have quite high cover, with C. stagnalis the only starwort.

Habitat

The C. stagnalis community can be found throughout lowland Britain in a variety of more shallow open waters with but sluggish flow or none, as in dykes, canals, ponds and even periodically rain-filled track ruts, and in such habitats conditions can be eutrophic with the substrates often of silt or clay. It is more distinctive, though, in quite fast to very swift, sometimes seasonal or spatey, waters in streams with sandy or gravelly beds, base-rich in those rarer situations where such conditions are met in the south-east of the country, more acidic and impoverished through the upland fringes of the west and north, where they become very common.