ocrea , auch: ochrea

Those species that do not have the nodal ocrea can be identified by their possession of involucrate flower heads.

They have persistent or deciduous ocrea.

The ocrea is not fringed.

The stems have nodes covered by an ocrea, a thin, paper-like membrane - a characteristic of the Polygonaceae family.

The leaves are lance-shaped and are connected at the node by a membranous sheath, or ocrea.

In some species the ocrea, a thin flange where the leaf meets the stem, is enlarged and harbors ants.

The specific epithet is derived from the Latin ocrěātus 'wearing greaves' from ocrea 'greave', referring to its loose, baggy volva.

In the USA, it is very similar to Pennsylvania smartweed, but Redshank has a fringe of hairs at the top of the ocrea, something which Pennsylvania smartweed lacks.

Ochrea, (Latin ochrea, greave or protective legging), also spelled ocrea, is a plant structure formed of stipules fused into a sheath surrounding the stem, and is typically found in the Polygonaceae.

On his right arm, he wore a manica (a heavy linen or metal wrapping tied with leather thongs), and on his left leg, he wore an ocrea (a greave made of boiled leather or metal).

While it superficially resemble bindweeds in the genus Convolvulus there are many notable differences; it has ocrea (stipule-sheath at nodes), which Convolvulus does not; and Convolvulus has conspicuous trumpet-shaped flowers while Black-bindweed has flowers that are unobtrusive and only about 4 mm long.

Around the stem of both these species there is a papery sheath known as a ocrea with stiff spine-like hairs at the top, but in P. caespitosum these hairs are much longer, as long as the visible portion of the ocrea, whereas in P. persicaria they are much shorter.