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Herbaceous or shrubby perennials. Stems decumbent or erect, terete to quadrate. Leaves opposite, sessile to petiolate; blades membranous to coriaceous, ovate to oblong, margins entire to sinuate to crenate, cystoliths present, 0.1-0.5 mm long. Inflorescences of dichasia in leaf axils (or in axil of 2 partially fused bracts forming a cupulate involucre) or of axillary and terminal dichasiate spikes, racemes, thyrses or panicles; dichasia alternate or opposite, 1(-3)-flowered, subtended by a leaf or a bract, sessile or pedunculate; bracts alternate or opposite, various, small and distant, linear or subulate to large, green or brightly colored, prominent or inconspicuous, margins entire (in the Guianas). Flowers homostylous, subtended by 2 bracteoles, sessile or pedicellate; calyx deeply 4-5-lobed, posterior lobe sometimes greatly reduced in flowers with 5 calyx lobes; corolla greenish, white, pinkish, red, or purplish, usually with white or colored markings on ridged palate of lower lip, tube cylindric to expanded distally, usually lacking a distinct throat, limb strongly zygomorphic, bilipped, upper lip usually shallowly 2-lobed (rarely entire), lower lip 3-lobed, corolla lobes imbricate in bud; stamens 2, inserted at various positions in corolla tube, exserted from mouth of corolla, anthers 2-thecous (1 theca rarely sterile), thecae equal or unequal in length, equally or unequally inserted or superposed, 1 or both with basal appendage (usually spurred or apiculate) staminodes absent; pollen subprolate to perprolate, 2-4-aperturate, apertures flanked on each side by 1-several rows of ± circular insulae, exine usually reticulate; ovary with 2 ovules per locule, style exserted from mouth of corolla, stigma lobes indistinct to distinct, when distinct equal to unequal in length. Capsules stipitate, retinacula present, septa with retinacula remaining attached to inner wall of mature capsule; seeds 2-4, variable, spheroidal to diskoid, occasionally reniform or obcordate.


Cosmopolitan present, Guianas present
Cosmopolitan genus of up to 600 species; it is the largest genus of the Acanthaceae and also the largest genus of the family in the Guianas with 20 species.


J. brasiliensis.


Growth rings absent.
Vessels more or less in radial distribution, c. 8% solitary, the remainder in radial multiples of 2-4 (10), over 100 per sq. mm, outline angular to round, 30 (18-50) µm wide. Vessel member length 340 (145-500) µm. Perforations simple, intervascular pits 3.5-4 µm, slits enclosed or confluent, giving the impression of spiral thickening; vessel/ray pitting identical. Tracheids occasionally present.
Rays exclusively 1-seriate, 16 per mm. All cells upright, juvenile type. Height up to 500 µm (6 cells).
Parenchyma extremely scarce, restricted to strands bordering a vessel. Strands fusiform and 2-3-celled.
Ground tissue of non-septate fibres. Diameter 12-15 µm, walls 3.5-4 µm thick. Pits simple, minute, in radial and less frequent in tangential walls. Length 550 (320-720) µm. F/V ratio: 1.60.