Geography and distribution
Acanthus syriacus is recorded from the easternmost extent of the Mediterranean, from southern Turkey through Lebanon, Syria and Palestine to Israel and Jordan.
Overview: Acanthus syriacus is a spiny perennial herb, 20 to 80 cm tall, with a spectacular terminal spike of large purple and white flowers.
Leaves: The leaves are clustered towards the base of the stems, often forming a loose rosette. The lower leaves are stalked whilst the uppermost leaves are sessile. The leaf blade is rather leathery and large, about 10 to 30 cm long, oblong or lance-shaped in outline but deeply lobed along its entire length. The lobes are toothed and spine-tipped, and the leaf surface is hairy mainly along the main veins and margin.
Flowers: The dense flowering spike is up to 60 cm long with the flowers arranged in opposite pairs. Each flower sits above a large purple or purple-green bract with a harshly spined margin and tip, the surface with prominent subparallel veins. The upper and lower sepals are large and rich purple-coloured, the upper sepal forming a prominent hood above the petals. The petals themselves are white or white-green in colour and are united into a short tube which splits dorsally to form a single 3-lobed lip. Four stamens protrude from the petal tube, each with a thick, bony filament and a hairy brush-like anther.
Fruits: The fruit is a four-seeded capsule, each seed sitting on a hook which assists in dispersing the seed as the capsule explodes open.
The Acanthus species of east Europe and the Middle East are closely related and can be difficult to separate, with their distinction sometimes clouded by hybridisation. Acanthus syriacus is no exception, being very closely related to the Turkish Acanthus hirsutus from which it differs largely in having purple, not green or yellowish, bracts and sepals, and in minor differences in stem and ovary indumentum (hairs). In the narrow zone of overlap in their ranges, some intermediate specimens have been collected, leading some botanists to treat A. syriacus as a subspecies of hirsutus.
Threats and conservation
This species is locally common within its restricted range and can be a prominent component of open ‘garrigue’-type vegetation on rocky hillslopes, a widespread habitat within its range.
It is also able to persist in disturbed habitats, its spiny foliage protecting the plant against grazing. However, as mature plants are unpalatable to domestic stock and potentially harmful due to their harsh spines, local farmers in some areas selectively remove plants when they are immature. It is therefore becoming increasingly scarce in some regions, for example in Lebanon where it has been highlighted as threatened by the Millennium Seed Bank project, staff from which have successfully collected the seeds as an ex-situ conservation measure.
Acanthus syriacus is grown as an ornamental herbaceous perennial. The leaf design was used by the Greeks in Corinthian columns.
Although less well known to gardeners than its close relatives Acanthus spinosus and Acanthus mollis, Acanthus syriacus nevertheless has much horticultural potential, with its spectacular flowers, more brightly coloured than the popular species, and its neat, compact habit. It is now widely available from horticultural specialists. However, although it can grow well in temperate gardens, it is perhaps less hardy than other widely grown Acanthus species, a reflection of its southerly, lowland native distribution. It can also suffer from excessive winter moisture.
Millennium Seed Bank: Seed storage
Kew's Millennium Seed Bank Partnership aims to save plant life world wide, focusing on plants under threat and those of most use in the future. Seeds are dried, packaged and stored at a sub-zero temperature in our seed bank vault.
Number of seed collections stored in the Millennium Seed Bank: Two
Seed storage behaviour: Orthodox (the seeds of this plant survive being dried without significantly reducing their viability, and are therefore amenable to long-term frozen storage such as at the MSB)
Germination testing: Successful
Composition values: Oil content 2.2 - 2.4%, Protein 22.4 - 24.9%
The challenges of seed collecting
A team from Kew and the Lebanese Agricultural Research Institute spotted six rare Acanthus syriacus plants by a road in 1998. They found no seeds that day, and returning the next year they found the plants diseased and damaged by insects. The team persisted and went back every year. Finally on their fourth visit they found ripe seeds to collect! These are now safely stored in Kew’s Millennium Seed Bank. This plant is one of the most difficult species for seed collecting because its spines are so hard and sharp.
This species at Kew
Kew's Herbarium houses numerous dried pressed specimens of Acanthus syriacus including two collected from Palestine in 1846 by the describer of this species, P. Edmond Boissier. P.E. Boissier (1810-1885) was a Swiss botanist and traveller, whose publications include the pioneering Flora orientalis.