Acanthaceae

Bear's Breech (Bear's Breeches, Oyster Plant), Acanthus mollis, is a native of southern Europe and the Mediterranean region, including Portugal, northwestern Africa and Croatia and is the national flower of Greece. Historically, it was also considered a possible native of the Isles of Scilly (Charles Babington, 1851 in The Annals and magazine of natural history; zoology, botany, and geology 8(2): 505-506). It is found in dry, rocky places. It is a popular garden place and naturalized in the British Isles, occurring in waste places, on roadsides and railway banks and in scrub; as seen here on the south coast of England.

The family Acanthaceae belongs to the Asterid group of eudicots and is closely related to the Lamiaceae (Mint Family). The fruit is a capsule that opens explosively and in one subgroup, the Acanthoideae, which includes Acanthus, an appendage called the jaculum or retinaculum, borne on the funiculum (the stalk attaching the ovule to the placenta of the ovary wall) responds to drying and helps propel the seed, increasing the dispersal distance to some 5 m. The genus Acanthus contains shrubs and perennial herbs.

The large (up to about 30 cm long) oppositely arranged leaves at the base of the stem of Acanthus mollis are stylized in the carved capitals of columns in Corinthian architecture (Athenian architecture dating to the 5th century BC and later used by the Romans) and also in the Composite order of architecture (a late Roman mixture of Ionic and Corinthian architectures). The leaves are pinnatifid and smooth, but with hairy margins and the lowest at least are borne on stalks.

The unbranched stems are up to about 1 m tall and terminate in flower spikes. The floral arrangement is curious. The petals (corolla) form a short horny/leathery tube with only the lower lip (labellum) forming an expanded limb (the flowers are said to be monopetalate - consisting of a single petal) subdivided into three lobes and colored white (often with purplish veins). There are 4 sepals, the upper and lower are well-developed and often tinged purple; the two lateral sepals are much reduced. The 4 protruding stamens occur in two pairs; each anther consists of a single theca (pollen chamber) and is borne on a long hard ('bony') filament that inserts at the top of the corolla tube.The anthers are 'bearded' that is they have a row of hairs on either side of the longitudinal slit where they split open to release pollen. The style is a long filament, extending beyond the anthers and terminating in a bilobed stigma. Each flower is subtended by three bracts (variously called bracts or bracteoles): two narrow lateral bracts and one large lower bract with a spiny margin. The fruit is a dark (when ripe) shiny capsule with 4 seeds (2 in each locule).

Lab = labellum (3 lobed lower lip of corolla); LB = lateral bract (x 2); LS = lateral sepal (x 2); LowB = lower bract; LowS = lower sepal; US = upper sepal. (This specimen was growing in Mount Ephraim Gardens, Kent, UK).

The genus Acanthus is found in Old World tropics and subtropics. Acanthus spinosus is a similar species to Acanthus mollis, but with slightly shorter stems (to 80 cm) and more deeply divided doubly pinnatifid leaves with spiny lobes. The lower bract also has more prominent marginal spines. This form occurs in southern Greece along the edges of fields and in stony wet places. The bracts are usually hairy.

Acanthus ilicifolius is an upright shrub up to 2 m tall that occurs in mangrove swamps and marshes near sea level and ranges from Cambodia to India to the Philippines to Australia and the Pacific Islands. It has spiny holly-like leaves (hence 'ilicifolius').