Mayo, S. J., J. Bogner & P. C. Boyce. 1997. The genera of Araceae. Royal Botanic Gardens, Kew.
106 genera and ca. 2500 spp.; cosmopolitan, but most diverse in the tropics, with many taxa widely cult. for ornament or food; 19 genera with 247 native or naturalized spp. in CR.
Terrestrial to epiphytic or hemiepiphytic herbs, rarely floating aquatics, acaulescent or stems rhizomatous to erect, appressed-climbing, or elongate-scandent. Leaves spiraled or distichous, some (cataphylls) reduced to the sheathing portion of the petiole. Petioles with or without a distal (rarely medial) geniculum (pulvinus). Leaf-blades simple to pinnately or bipinnately lobed to pedately or palmately compound, usually glabrous, the margins entire or (very rarely) serrate. Plants hermaphroditic or monoecious, the infls. morphologically terminal (though often appearing axillary) spadices, each subtended to enclosed by a single, often colored spathe. Fls. always much reduced and usually crowded, bisexual or unisexual (with female fls. borne proximally and male fls. distally on each spadix), ± actinomorphic, ebracteate; ± differentiated sterile fls. often present, i.e., at base of hermaphroditic infls. or between male and female regions of monoecious infls. Perianth members (tepals) lacking (hermaphroditic and some monoecious spp.) or 4-6+, similar, greenish to brownish or purplish, distinct or (rarely) connate. Stamens 2-6+, distinct or connate as synandria (some unisexual fls.); ± modified staminodia often present in female fls., where sometimes connate as synandrodia. Pistil 1, compound or pseudomonomerous; ovary superior, with 1-3(-14+) locules; style 1; stigma ± discoid; ovules 1-numerous per locule; placentation axile, parietal, basal, or apical. Fr. a 1-numerous-seeded berry.
In CR, the Araceae are most abundant and diverse in lowland wet forest and cloud forest habitats. The family is generally easily recognized by its ± succulent stems and petioles, thickish, usually glabrous, entire-margined leaf-blades often with ± reticulate, dicot-like venation, and characteristic (spathe and spadix) infls.
Throughout this family account, leaf-blade length is measured from the posterior margin (including any posterior lobes) to the apex (or apex of the anterior or medial lobe).
1 Floating aquatics with subsessile, spongiose leaves in dense rosettes; infls. < 2 cm long...Pistia
1' Plants not aquatic or, if so, firmly rooted; leaves petiolate, not rosette-forming; infls. usually > 2 cm long.
2 Leaves peltate.
3 Stems erect, to ca. 0.75 m tall; leaf-blades coriaceous, glossy, plain green...Alocasia
3' Stems cormose, subterranean; leaf-blades thin, matte or dull, often colorfully marked.
4 Leaf-blades usually with cream to pinkish or reddish blotches or spots; plants with milky sap; spadix lacking sterile terminal appendage...Caladium
4' Leaf-blades usually ± plain green, but often with purplish adaxial blotch over petiole insertion; plants with reddish sap; spadix with sterile terminal appendage...Colocasia
2' Leaves not peltate, or scarcely so (or leaves absent at anthesis).
5 Leaf solitary, the blade divided into 3 main sections which in turn are subdichotomously divided into narrow segments; stem cormose...Dracontium
5' Leaves > 1 (or absent at anthesis); leaf-blades simple or pinnately or bipinnately lobed to pedately or palmately compound.
6 Fls. bisexual, with or without perianth; spadix ± uniform, not differentiated into proximal female and distal male portions; spathe deflexed to erect, not differentiated as proximal tube and distal lamina; leaves spiraled or distichous.
7 Spathe ± persistent; fls. with perianth.
8 Spathe reflexed to erect, not enveloping the spadix at anthesis, the margins not or scarcely overlapping; plants terrestrial or epiphytic; petioles with geniculum.
9 Plants epiphytic or (occasionally) terrestrial, then usually with a ± evident stem; leaves spiraled; leaf-blades simple or palmately or pedately compound, when simple linear to sagittate; tertiary leaf veins usually reticulate; tepals 4, distinct...Anthurium
9' Plants terrestrial, acaulescent; leaves distichous; leaf-blades simple, lanceolate to elliptical; tertiary leaf veins parallel; tepals 6 and distinct, or fused into a cup...Spathiphyllum
8' Spathe erect and enveloping the spadix at anthesis, the margins overlapping at least proximally; plants terrestrial; petioles lacking a geniculum.
10 Stems cormose; mature leaves lacking; acumen of spathe not spirally twisted; forest plants...Dracontium
10' Stems rhizomatous; mature leaves present, the blades simple and sagittate; acumen of spathe spirally twisted; swamp plants...Urospatha
7' Spathe promptly deciduous following anthesis; fls. lacking perianth.
11 Leaf-blades perforate and/or pinnately lobed...Monstera
11' Leaf-blades without perforations, simple and entire.
12 Petiole < 1.5 cm long, without geniculum; canopy vines...Heteropsis
12' Petiole > 1.5 cm long, with geniculum; terrestrial herbs to appressed hemiepiphytes or canopy vines.
13 Plants short-stemmed, epiphytes; leaves spiraled, the blades ± coriaceous, with primary lateral veins obscure, strongly ascending; peduncles at anthesis ± nodding distally...Stenospermation
13' Plants long-stemmed, appressed-climbing hemiepiphytes to canopy vines (or rarely terrestrial); leaves distichous, the blades membranous to coriaceous, with primary lateral veins usually conspicuous and spreading; peduncles at anthesis straight.
14 Primary lateral leaf veins usually relatively few and distant, rarely numerous and closely parallel (in which case the petioles are lenticellate-roughened toward the base); spadix sessile; placentation basal, the ovules 2 per locule; seeds 5-22 mm long, globose to oblong...Monstera
14' Primary lateral leaf veins numerous, ± closely parallel; petioles smooth; spadix sessile to stipitate; placentation axile, the ovules numerous, superposed; seeds 1-1.6 mm long, compressed...Rhodospatha
6' Fls. unisexual, without a perianth; spadix clearly differentiated into proximal female and distal male portions (often with medial and/or distal sterile zones as well); spathe erect and usually clasping, usually differentiated into a proximal tube and distal lamina; leaves spiraled.
15 Plants scandent or epiphytic.
16 Cut stems and petioles not exuding milky sap (sap rarely becoming whitish after exposure); leaf-blades simple to trifoliolate or bipinnately lobed, never (in ours) pedately compound, the tertiary veins ± parallel to reticulate; stamens and frs. distinct...Philodendron
16' Cut stems and petioles exuding copious milky sap; leaf-blades simple to trifoliolate or pedately compound, the tertiary veins anastomosing; stamens connate in synandria; frs. connate to form a syncarp...Syngonium
15' Plants terrestrial.
17 Leaf-blades pedately compound; plants with milky sap.
18 Stems terete, decumbent to erect; spadix relatively slender, the female portion fused proximally with spathe; sterile male fls. subprismatic, not elongate; Atl. slope and near Continental Divide...Chlorospatha
18' Stems cormose; spadix relatively stout, not fused with spathe (or only at very base); sterile male fls. elongate-prismatic; Pac. slope...Xanthosoma
17' Leaf-blades simple; plants with or without milky sap.
19 Leaf-blades lanceolate to elliptical, attenuate to acute, rounded, truncate, or (rarely) cordulate at base (but without prominent posterior lobes), often mottled or blotched with cream or yellowish.
20 Plants with decumbent to erect stems, usually with milky sap; foliage often with fetid odor; female portion of spadix proximally fused to spathe; stamens connate in synandria; female fls. with distinct staminodia...Dieffenbachia
20' Plants acaulescent, without milky sap; foliage usually with strong, ± pleasant odor; female portion of spadix free from spathe; stamens distinct; female fls. lacking staminodia...Homalomena
19' Leaf-blades ovate to sagittate, with prominent posterior lobes, plain green.
21 Leaves puberulent to pubescent, at least on distal portion of petiole and abaxially on leaf-blade midrib and major veins.
22 Plants lacking milky sap; petioles sometimes prickly at base; stamens distinct; female fls. usually with evident staminodia...Homalomena
22' Plants with milky sap; petioles never prickly; stamens connate in synandria; female fls. lacking staminodia...Xanthosoma
21' Leaves glabrous.
23 Primary lateral leaf veins ± close, the tertiary venation parallel and obscurely anastomosing.
24 Plants with brief decumbent to suberect, above-ground stems; leaf-blades cordate; spathe closed, the margins overlapping to at least the middle (differentiated into a basal greenish or reddish tube and a distal greenish to whitish lamina); female fls. lacking staminodia; forests at 0-2400 m...Philodendron
24' Plants acaulescent; leaf-blades sagittate; spathe broadly splayed, pure white, the margins overlapping only at very base (tube scarcely differentiated); pastures at 1200-3000 m; female fls. with conspicuous staminodia...Zantedeschia
23' Primary lateral leaf veins ± distant, the tertiary venation coarsely and conspicuously anastomosing.
25 Plants with elongate, erect, prickly stems; milky sap lacking; stamens distinct; plants of coastal swamps and estuaries...Montrichardia
25' Plants acaulescent or with stout, erect, ± smooth stems; milky sap present or lacking (present in caulescent spp.); stamens connate in synandria; plants of various habitats.
26 Plants with reddish sap; leaf-blades glossy, the apex directed skyward; crushed foliage with distinct cyanide odor; spadix with sterile distal appendage...Alocasia
26' Plants with milky sap; leaf-blades matte or dull, the apex directed earthward; crushed foliage without cyanide odor; spadix lacking sterile distal appendage...Xanthosoma