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(Last Modified On 10/25/2012)
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(Last Modified On 10/25/2012)
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Family
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ARACEAE
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Contributor
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PAUL C. STANDLEY
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Description
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Terrestrial or epiphytic plants, very rarely aquatic, herbaceous or often with elongate, suffrutescent caudices, frequently scandent by aerial roots, the terres- trial forms sometimes with tuberous roots, the caudices usually simple but some- times branched, the foliage glabrous or very rarely pubescent, the sap watery or milky, often caustic; leaves solitary or few in the tuber-bearing plants, in caulescent ones alternate and distichous, or spirally arranged, very variable in form; cataphylls usually present, these narrow, membranaceous, often carinate, sheathing the peduncles or petioles; peduncles simple, terminal or axillary; flowers small, perfect and all alike or unisexual, arranged upon a cylindric, usually elon- gate spadix, this subtended by a spathe, the spathe various in form, persistent or deciduous, often colored; pistillate flowers, in unisexual plants inserted on the lower part of the spadix, the staminate on the upper portion; perianth usually none in the unisexual flowers, in the perfect flowers of 4-6 segments, these cuneate or obovate, truncate or incurved at the apex, imbricate or rarely connate; stamens in the perfect flowers 4-8 and distinct, hypogynous, opposite the perianth segments, the filaments dilated, the anthers terminal, dehiscent by dorsal pores or slits; stamens of the unisexual flowers 1 to many, distinct or united to form a peltate, prismatic, or sinuate synandrium truncate at the summit; ovary entire or very rarely lobate, sessile or immersed in the spadix, 1- to many-celled; style none, or short or elongate, terminal, simple, the stigma terminal, discoid, pulvinar, or capitate, sometimes sessile along the apex of the ovary and linear-oblong or rarely lobate; ovules solitary or numerous in each cell, sessile or affixed by a short or elongate funicle; fruits baccate, numerous in each spadix, free or connate, indehiscent, or suboperculate by the separation of the thickened apex, the cells usually filled with glutinous or mucilaginous, pulp; seeds small or large, smooth or variously roughened, the endosperm commonly abundant and fleshy, rarely none.
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Note
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The family is essentially a tropical one,.abundantly represented in almost all warmer parts of America. A few genera besides those listed here are known from Central America. The group is a well-marked one, whose flower structure may be studied most conveniently, perhaps, in the common calla, Zantedeschia aethiopica (L.) Spreng., grown as commonly in Central America as in the United States. A noteworthy feature of the family is the presence in the foliage of needle-like crystals of calcium oxalate. If a piece of a leaf is chewed, these crystals penetrate the tongue, producing a burning sensation and swelling, the irritation sometimes persisting for many hours. Most of the Panama Araceae are epiphytic plants, and they form a large per- centage of the more conspicuous epiphytic vegetation upon trees of the humid lowlands, being rivaled in abundance only by the bromeliads. The foliage often is handsome and ornamental, and the inflorescences of many species are showy. While most of the plants thrive best in shade, their succulent leaves enable them to live in abundant sunshine. The literature of the Araceae is very extensive, chiefly because they have long been favorite plants in European hot-houses. The most recent and by far the most comprehensive monograph is that of Engler and Krause, Pflanzenreich IV. 23. Upon this the following treatment is based. In Central America the family is still but incompletely known, for lack of adequate herbarium material. The plants are succulent and difficult to dry and consequently are neglected by collectors. Moreover, although plants of a given species may be abundant, often it is difficult to find one with inflorescences. It may be stated that when named material is available for comparison, usually it is possible to name specimens from leaves alone. A study of the development or life history of the Panama plants of the family would be instructive and useful from several aspects. Especially in such genera as Monstera and Philodendron, the juvenile and adult forms are so different that at first glance one never would associate them. The connecting forms are -known or described in but few instances, therefore it often is impossible with present knowledge to name juvenile plants, although it is probable that all of them could be named if their variations were described.
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Key
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a. Plants aquatic, floating on the surface of water; leaves spongy, arranged in a basal rosette; inflorescence minute and scarcely visible -1. PIsTIA aa. Plants terrestrial or epiphytic; leaves not spongy, never arranged in a rosette; inflorescence large and conspicuous. b. Leaves peltate, spotted with white or various colors. Plants terres- trial, naturalized; flowers unisexual, naked - 7. CALADIUM bb. Leaves not peltate, green. c. Leaf blades perforated, sometimes also pinnatifid. Flowers perfect_ 4. MONSTERA cc. Leaf blades not perforated. d. Leaves digitately compound, pedately 3- to 11-cleft, pinnatifid, or trilobate almost or quite to the base. e. Blades two or more times divided, with very numerous small segments. Plants terrestrial; leaf 1; flowers perfect, with a perianth -6. DRACONTIUM ee. Blades only once divided or cleft. f. Leaves pinnatifid. Plants epiphytic, with elongate caudices; perianth none. g. Flowers perfect, the spadix uniform -4. MONSTERA gg. Flowers unisexual, the upper part of the spadix with staminate flowers, the lower with pistillate -15. PHILODENDRON ff. Leaves trilobate, trisect, or pedately or digitately 5- to 11- parted. g. Spathe spreading from the base of the spadix; flowers with a perianth - 2. ANTHURIUM gg. Spathe, at least the lower portion, enclosing the spadix; perianth none. h. Leaves triparted or trisect. Plants epiphytic, with elongate caudices. i. Blades triparted to the base -15. PHILODENDRON ii. Blades trisect almost to the base - 14. SYNGONIUM hh. Leaves pedately cleft, with 5 or more segments. i. Plants terrestrial, arising from a tuberous caudex - 8. XANTHOSOMA ii. Plants epiphytic, with elongate caudices -14. SYNGONIUM dd. Leaves simple and entire, often cordate or hastate-lobate at the base. e. Flowers all or mostly perfect, the spadix uniform, not divided into a pistillate and a staminate portion. f. Plants terrestrial, acaulescent. g. Leaf blades acute to rounded at the base -5. SPATHIPHYLLUM gg. Leaf blades hastate, with elongate basal lobes -3. UROSPATHA ff. Plants epiphytic, at least normally so, usually with a well- developed caudex. g. Stigma discoid; plants with short or elongate caudices 2. ANTHURIUM gg. Stigma oblong or linear; plants with elongate, scandent caudices. h. Peduncles cernuous or recurved at the apex at or be- fore anthesis _- - __ - _ _ 13. STENOSPERMATION hh. Peduncles erect at the apex. i. Lateral nerves of the leaves reticulately anasto- mosing, the secondary and tertiary ones not parallel with the primary ones - 4. MONSTERA ii. Lateral nerves of the leaves all more or less parallel, not anastomosing. j. Ovary 2-celled --- 10. RHODOSPATHA jj. Ovary 2- to 6-celled - 12. ANEPSIAS ee. Flowers unisexual, the spadix with two distinct portions, the lower pistillate, the upper staminate. Perianth none. f. Plants epiphytic, at least normally *so, the caudices more or less elongate and rooting at the nodes -15. PHILODENDRON ff. Plants terrestrial, acaulescent, or with erect caudices sup- ported by prop roots. g. Leaf blades chiefly oblong, rounded to very shallowly cordate at the base ---9. DIEFFENBACHIA gg. Leaf blades hastate or cordate, with a deep basal sinus. h. Plants glabrous. i. Caudex erect, usually prickly and supported by prop roots - ---------_ - 16. MONTRICHARDIA ii. Caudex hypogean, tuberous -_ 8. XANTHOSOMA hh. Plants pubescent. i. Stamens distinct --- 11. HOMALONEMA ii. Stamens connate to form a 5- to 6-angulate synandrium ----- 8. XANTHOSOMA
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