Appressed hemiepiphytic climbers or vines, less frequently terrestrial, rarely true epiphytes; sap usually tanniniferous, drying dark, rarely with latex, drying white; caudices densely rooted at nodes; juvenile plants usually terrestrial and scandent, the petioles conspicuously sheathed; adult plants with intenodes short to elongate, sometimes flattened on one side; cataphylls unribbed or variously ribbed, persistent or deciduous, remaining intact or more usually weathered to fibers; petioles short or more usually elongate, usually sheathed only at base (except sect. Pteromischum), variously shaped in cross-section, firm or spongy; blades simple and entire, ovate to oblong or elliptic or variously divided, trisect, palmatisect or pinnatifid; midrib raised or sunken above, raised below; primary lateral veins conspicuous, spreading to the margins, not forming collective veins, the lowermost primary lateral veins often coalesced on cordate blades, the posterior rib, naked with the sinus or not; interprimary veins sometime present; minor veins conspicuous or obscure, usually fine and closely parallel; cross-veins sometimes visible; laticifers sometimes appearing like veins; INFLORESCENCES 1-several per axil, much shotter than the leaves; peduncles shorter or longer than the spathe; spathe convolute at base, persistent, usually coriaceous, frequently colorful, often bicolorous on outside, less frequently so within, typically somewhat constricted above the tube, opening widely at anthesis, then reclosing and persisting in fruit; spadix divided into pistillate and staminate portions, each with unisexual flowers; pistillate portion basal, usually much shorter than the staminate portion, usually greenish; staminate portion clavate, white, usually somewhat constricted above the sterile staminate portion (at base). Flowers naked, closely aggregated in several spirals; staminate flowers consisting of 2-6 sessile stamens united into a synandrium truncate at apex and usually irregularly 4-5-sided; thecae oblong or linear, emarginate at the base, each opening by short slits; pistils ovoid to obovoid, 2-several-celled; ovules 1 to several to numerous per locule, orthotropous or half anatropous, ascending on moderately long funicles; stigma sessile, funnel-shaped or bmsh-like and hemispherical to lobulate. INFRUCTESCENCES with berries cylindroid, exposed by the reopening of the spathe; seeds few to many per berry, oblong to elipsoid or ovoid-oblong; the testa rather thick, striate-costate; endosperm present. Species ca. 700,
HABIT : evergreen herbs, small to gigantic, stem repent to rhizomatous, climbing, arborescent or plant rosulate and acaulescent, internodes usually long, often short to very short, intravaginal squamules present, sometimes producing flagelliform shoots. LEAVES : numerous, small to gigantic, prophylls of mature stems caducous, marcescent and deciduous or persistent and membranaceous or decomposing to net-fibrous remains. PETIOLE : sometimes warty or covered with scale-like processes, sometimes swollen, rarely geniculate apically, sheath long and slilghtly ligulate in monopodial leaves of all subgenera and in sympodial leaves of subgen. Pteromischum, otherwise very short and inconspicuous except when subtending inflorescences. BLADE : very variously shaped; simple and linear, cordate, sagittate or hastate, or trifid, trisect, pinnatifid, bipinnatifid, rarely pedatisect, resin glands linear, short to long, obscured to very distinct on abaxial surface; basal ribs sometimes well-developed, primary lateral veins pinnate, rarely pedate, running into marginal vein, secondary lateral and higher order venation parallel-pinnate, sometimes tertiaries and higher order veins transversely reticulate between secondaries, sometimes all veins slender with no distinct primary laterals. FLOWERING BRANCHES : sympodial articles of three main patterns :- subgen. Pteromischum : prophyll, many foliage leaves, 1-2(-3) inflorescences; subgen. Philodendron : prophyll, following internode suppressed, 1 foliage leaf, 1-11 inflorescences, internode to prophyll of continuation shoot elongated; subgen. Meconostigma : prophyll, following internode developed or very short, 1 foliage leaf, 1(-2) inflorescence, internode to prophyll of continuation shoot suppressed. INFLORESCENCE : 1-11 in each floral sympodium, secreting resin at anthesis, either from spathe or from spadix, rarely from both. PEDUNCLE : usually much shorter than petiole. SPATHE : erect, entirely persistent, deciduous only at ripening of fruit (caducous after anthesis in P. surinamense), fairly thick, sometimes (subgen. Meconostigma) extremely thick, usually constricted between tube and blade, tube convolute, cylindric to ventricose, often coloured purple or red within, blade usually boat-shaped, widely gaping at anthesis, later closing, usually white within, rarely red. SPADIX : sessile to stipitate, female zone free, rarely basally adnate to spathe, usually shorter than male zone and separated from it by intermediate sterile zone of staminodial flowers, intermediate sterile zone cylindric or constricted or ellipsoid and thicker than male zone, usually shorter than male zone, sometimes longer (subgen. Meconostigma), a terminal staminodial appendix sometimes also present. FLOWERS : unisexual, perigone absent. MALE FLOWER : 2-6-androus, stamens free, prismatic to obpyramidal, sometimes very elongated and slender (subgen. Meconostigma), anthers sessile to subsessile, connective thick, apically truncate, overtopping thecae, thecae ellipsoid to oblong, dehiscing by short lateral slit or by subapical pore, endothecial thickenings lacking (except P. goeldii, P. leal-costae). POLLEN : extruded in strands or mixed with resin secretion or exuded in amorphous masses, inaperturate, ellipsoid to oblong or occasionally elongate, medium- sized (mean 40 µm., range 28-54 µm.), mostly perfectly psilate, sometimes from minutely verruculate, scabrate or fossulate to clearly punctate, subfossulate, subfoveolate or subverrucate, rarely densely and coarsely verrucate (P. leal-costae). STERILE MALE FLOWERS : staminodes usually prismatic, truncate, sometimes clavate, often somewhat similar to stamens. FEMALE FLOWERS : gynoecium ovoid, subcylindric, cylindric or obovoid, ovary (2-)4-8(-47)-locular, ovules 1-50 per locule, usually hemiorthotropous, rarely hemianatropous to nearly anatropous, funicles long to very short, placenta axile to basal, stylar region usually as broad as ovary, sometimes slightly broader, sometimes attenuate, rarely elongate, lobed in subgen. Meconostigma, stigma sometimes also lobed or discoid-hemispheric, often as broad as style. BERRY : subcylindric to obovoid, 1-many-seeded, white, whitish- translucent, red or orange-red. SEED : tiny to fairly large, ovoid-oblong to ellipsoid, rarely arillate (in P. goeldii funicle thick, swollen, much larger than seed itself), testa thick, costate, rarely sarcotestate, embryo axile, straight, elongate, endosperm copious.
Evergreen, small to gigantic, mostly climbing hemiepiphytes or epiphytes, sometimes arborescent to rhizomatous terrestrials; leaves with abundant resin canals; leaf blade very variable in shape, from linear to bipinnatifid, trisect or pedatisect, lacking a submarginal collective vein, fine venation parallel-pinnate; inflorescence secreting resin from spathe or spadix at anthesis; endothecium nearly always lacking cell wall thickenings; flowers unisexual, perigone absent; ovary usually 4-8-locular (extreme range 2 to 47-locular); ovules usually hemiorthotropous; placenta axile to basal. Differs from Anthurium in unisexual flowers without perigone, and parallel-pinnate fine venation.