Description

Key Characters:

Growth Form: Non-aromatic perennial herbs, lianas, or subshrubs.

Stems: Stems erect to decumbent, quadrangular, many-branched or occasionally only sparingly so, usually pubescent.

Roots:

Leaves: Leaves simple. Opposite. Surfaces variously pubescent and also usually glandular–dotted (the glands amber and often inconspicuous when fresh, more conspicuous in dried material, turning white or black in old dried material); blades membranous to occasionally subcoriaceous, smooth to rugose. Petiolate. Stipules absent.

Flowers: Flowers 1–14 or rarely more per verticillaster, on short or elongate pedicels, rarely these on a common peduncle, arranged in terminal, bracteate, racemose inflorescences on the main and lateral stems, either simple and unbranched or compound, formed by the principal inflorescence flanked by smaller secondary or even tertiary, lateral, racemose inflorescences, or in P. floribunda only on short, congested, lateral branches arising in the axils or below the lowermost leaves. Calyx usually obconical or campanulate, enlarging in fruit, the teeth increasing only in width, usually 5-toothed, splitting longitudinally, usually persistent or sometimes only ventral 1/2 persistent. Corolla bilabiate, white or sometimes tinged pink or purple, rarely pink or in P. floribunda red, tube narrowly funnelform, usually curved, upper lip entire or 2-lobed, flat or concave, lower lip larger, 3-lobed, lateral lobes ovate, slightly asymmetrical, lower lobe broadly ovate to suborbicular, slightly folded to form a groove, margins somewhat undulate, apex emarginate or entire; nectary disk often present at base of ovary, annular or developed on anterior side only. Stamens 4, both pairs of similar length or upper pair slightly longer, ascending the upper corolla lip, included, aligned with the sinuses; filaments inserted near throat, usually pubescent; anthers dithecal, opening by longitudinal slits; anther sacs divaricate. Ovary superior, 2-carpellate, placentation basal-axile; ovules 1 per ovary lobe; style 1, included, arising between lobes, shortly 2-lobed, the lobes clavate; stigmatic only at apex, 1 lobe often rudimentary; stigmas 2.