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|Inflorescence of Acanthus mollis|
Acanthus mollis, commonly known as bear's breeches or oyster plant, is a herbaceous perennial plant with an underground rhizome in the genus Acanthus. It is regarded as an invasive species in some jurisdictions. , 
The name of the genus derives from the Greek term ἄκανθα ("ákantha") meaning "thorn", referring to the thorn-bearing sepals, while the Latin name of the species, "mollis" meaning "smooth", refers to the texture of the leaves.
Acanthus mollis reaches on average 30–80 centimetres (12–31 in) of height, with a maximum of 180 centimetres (71 in), inflorescence included. It has basal clusters of deeply lobed and cut, shiny dark green leaves, soft to the touch, up to 40 centimetres (16 in) long and 25 centimetres (9.8 in) broad, with a long petiole. The inflorescence is a cylindrical spike 30–40 centimetres (12–16 in) long and can produce up to 120 flowers. The flowers are tubular, whitish, and lilac or rose in colour. Each flower is up to 5 centimetres (2.0 in) long and it is surrounded by three green or purplish bracts. The central bract is spiny and larger than the other two. The calyx has two lips: the upper is purple on top, rather long and forms a kind of "helmet" on top of the corolla. The corolla is reduced to a white lower lip, trilobed, with purple-pink venation. The four stamens are fused to the corolla and look like tiny brushes. This species flowers in late spring or early summer, from May through August.
Acanthus mollis is entomophilous and it is pollinated only by bees or bumble bees large enough to force their way between the upper sepal and the lower, so that they can reach the nectar at the bottom of the tube. The fruit is an ovoid capsule containing two to four large black seeds. The dispersal of seeds is by the wind (anemochory).
These plants are usually propagated from tubers and tend to form large, localized clumps which can survive for several decades and look statuesque when well-grown, but its suitability as a garden plant is lessened on account of its invasive nature (new plants are produced readily both from seed and portions of root) and its susceptibility to powdery mildew and attacks from snails.
This garden plant is also quite common in the wild. It grows in dry areas, roadsides and wastelands, especially in the rocky and bushy places. It is tolerant of drought and shade and generally does not exceed an altitude of 300 metres (980 ft) above sea level.
- Vitruvius. On Architecture. Book IV.
- Pierre Delforge - Orchids of Europe, North Africa And the Middle East - 2006, Timber Press
- Pignatti S. - Flora d'Italia (3 voll.) - Edagricole – 1982, Vol. III
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- The Introduced Flora of Australia and its Weed Status, by R.P.Randall, Department of Agriculture and Food, Western Australia 
- Acanthus mollis in the Canary Islands
- Malta Wild Plants
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