A Brief Introduction to Equisetum

- originally produced as a leaflet for the NCCPG Plant Heritage exhibit at the Hampton Court Flower Show, 1999.

The genus Equisetum ('Horsetails') are the survivors of a major division of the plant world, quite distinct from other groups such as flowering plants, conifers and ferns. Our present day plants are little changed from their ancestors that grew 100 million years before the Dinosaurs.

With their unique 'architecture' and almost alien appearance they make fascinating subjects for study, curiosity and ornament.

Evolution
Equisetum is the sole surviving genus of the class Sphenopsida, which in the Carboniferous period included tree-like forms, growing to over 30m, such as the Calamites whose fossil remains are a major contributor to the coal measures. These plants were similar in form to the modern Equisetum, differing mainly in their size, the degree of branching and the existence of secondary ('woody') thickening of the stems.

Fossils show smaller plants difficult to distinguish from modern Equisetum as early as the Triassic period (about 230 million years ago) and possibly the Carboniferous period (about 320 million years ago)

Distribution, Habitats and Habit
Today there are about 20 species, with a world-wide distribution.

They typically grow in wet places, ponds, marshes, wet woodland and the banks of lakes and rivers, but also in drier ground where their deep running rhizomes can reach moisture.

All the Equiseta are herbaceous perennials, the aerial shoots of the sub-genus Hippochaete being more or less evergreen and those of the sub-genus Equisetum quickly dying back to the ground after frost. The aerial shoots grow from similar but specialised underground rhizomes that are the primary means of spread. Most species have radial branching and reduced leaves at the branching nodes. They vary in height from 0.15m up to 13m although most are about 0.5m to 1.5m high. Cones are formed at the top of some aerial shoots which disperse spores from which tiny separate gametophytes grow in a similar way to those of ferns.

Cultivation
Most species of Equisetum can be grown either in pots or in the open ground. Many gardeners may feel that the former is much the wiser approach! In practice, however, it is only E. arvense that is likely to be invasive and cause a problem by their spread in most garden conditions (although E. telmateia, palustre and fluviatile can need control in certain more extreme soil conditions).

Cultural needs are mostly undemanding, being happy in a wide range of soils, providing there is sufficient moisture within reach of the rhizomes. When grown in pots, it is best to stand them in trays of water, about 50mm deep to reduce the otherwise serious risk of completely drying out.

They will grow in sun or shade but those with no shelter tend to look somewhat battered by late summer.

Equiseta are most easily propagated by division of the underground rhizomes - a small section with at least one visible 'bud' at a node will usually establish itself. Sufficient moisture is even more important at this stage.

They can also be grown from spores in much the same way as ferns, but the spores are green and must be sown within a few days of shedding.

Equisetum in the Garden
Although most people are likely to grow Equisetum species out of botanical interest or curiosity, a number will make good subjects for the non-specialist garden.

E. hyemale var. affine (often sold as E. robustum) produces clusters of largely unbranched subtly variegated shoots, tipped with black cones, up to 2m long, providing a plant of strong sculptural character, useful as a focal point in a damp garden or pond-
side.

E. telmateia can also grow up to 2m, with bottle-brush whirls of 30cm diameter in summer. Its large primeval-looking cones appear in spring, providing alternative fascination in the bulb season. It can look marvellous when established in stands alongside streams, ditches or ponds (a visit to Cambridge Botanic Gardens is recommended!).

E. sylvaticum, by contrast, is a delicate little plant, only 30-50cm tall, with branched whirls, often fondly described as 'miniature Christmas trees', suitable for shady areas such as the edge of woodland gardens.

E. fluviatile, the only true aquatic Equisetum, can have branched or straight stems of up to 90cm; an 'must' for large 'wildlife' ponds but visually useful and controllable in small ponds.

E. scirpoides, is a prostrate-growing alpine with pretty twisted dark green stems emphasized by the black cones at the ends, superb against a gravel background.