Croat T. B., 1988, Ecology and Life Forms of Araceae, Aroideana 11(3-4)

4 AROIDEANA, Vol. 11, No.3 Ecology and Life Forms of Araceae Thomas B. Croat Missouri Botanical Garden RO.Box299 st. Louis, Missouri 63166-0299 INTRODUCTION casts a darker shadow) where a physio Araceae, a family of herbaceous mono logical change takes place allowing them cotyledons with 106 genera, is a com to grow toward light (Strong & Ray, plex group in terms of life form and 1975). They grow as appressed epi ecology. The family is widespread, with phytes on trees or as vines in the canopy. almost an equal number of genera in Others begin their lives as true epi both the Old and New Worlds, but with phytes, some reconverting to hemiepi the majority of species occurring in the phytes by producing long, dangling roots New World tropics. A few genera range contacting the forest floor below. into north temperate regions with one species ranging to at least 63 degrees Some species, especially members of north latitude. Few aroids range into subfamily Monsteroideae, have heterob temperate regions of the southern hemi lastic development with leaf and stem sphere; the most southernly being Pistia morphology reflecting the differences in stratiotes L., which can be found through their growth phases. Juvenile plants may 36 degrees south latitude in Argentina. produce a small terrestrial rosette of The family occupies a wide variety of life leaves, then grow rapidly, producing a zones and habitats throughout its range, few small leaves on long internodes. The extending from tropical dry to pluvial preadult leaves of the first hemiepiphytic rainforest, but also ranges into subarctic phase of such plants are often very marshes, tropical swamps, cloud forests, distinct from the adult leaves. Many such cold windswept montane plains and species are able to convert again and semi-arid to arid coastal plains. The again from adult growth (consisting of family has many species which will not short, thick internodes) back to juvenile tolerate any degree of frost or cold such growth (with elongate internodes bear as Anthurium brownei Masters, as well ing smaller leaves), either to establish as some, like Symplocarpus foetidus (L.) more adult plants with a rosette of leaves Nutt., which actually emerge from snow or to survive the dynamics of an ever covered ground. changing forest, complete with treefalls The most interesting aspect of the and falling branches (Ray, 1987). Other family's ecology is the diversity of adap hemiepiphytic species are vines which tive life forms. These range from sub branch and produce growth throughout merged to free-floating, and emergent the lower and middle levels of the aquatics to terrestrial plants and to canopy. These species (e.g., Philoden epilithic or epiphytic forms which may dron scandens K Koch & Sellow) ac be true epiphytes or hemiepiphytic complish long-term survival by having a (growing on trees but rooted in soil). portion of their biomass in a part of the Hemiepiphytism is diverse itself, with canopy which survives any particular some species beginning their lives as treefall (Pefialosa, 1975). Even true epi terrestrial seedlings, then growing phytes rarely succumb promptly to a fall skototropically (toward darkness) until from their host tree, but instead con they arrive at the nearest suitable tree tinue to flower and fruit on the ground ( usually a relatively large one which for a limited time. T. Croat, 1988 5 DISCUSSION by only one genus, with one pantropic The following is an outline and discus and variable species. Pistia stratiotes L. sion of life form diversity in the Araceae has a short stem and a rosette of (see Appendix III for a glossary of aerenchymatous, buoyant leaves, with a terms): cluster of fine, hair-like roots below. It 1. Aquatic plants occurs mainly at lower elevations and 1.1 Submerged aquatics inhabits mostly open, fresh waters at the 1.2 Free-floating aquatics edges of slow-moving streams, lakes and 1.3 Emergent aquatics ponds. This species is remarkably suc 2. Terrestrial plants cessful in using mostly vegetative repro 3. Epilithic plants duction, often totally clogging small to 4. Epiphytic plants large waterways in a short period of 4.1 Hemiepiphytes time. Vines Appressed climbers 1.3 Emergent Aquatics 4.2 Epiphytes Emergent aquatiCS make up a very large group within Araceae. Many genera 1.1 Submerged Aquatics have at least some species which spend Jasarum steyermarkii Bunting has per all or part of their lives rooted in manently submerged leaves and is the standing or moving water. Temperate only true example of this life form North America is particularly rich in among neotropical Araceae. It grows aquatiC or semiaquatic genera. Most, rooted in moving streams on the escarp including Acorus, Calla, Lysichiton, ment of the Guayana Highland where it Orontium, Peltandra and Symplocar is endemic (Bogner, 1985). When it pus, grow in swampy or marshy areas, flowers, the scape is protruded above lakes, ponds, or along the edges of the level of the water. Many rheophytes, creeks. Arisaema triphyllum (L.) Torr. however, may spend a portion of their is also reported as sometimes occurring lives underwater with no apparent harm, in swampy areas (Small, 1933; Correll & but flowering occurs when the plants are Correll, 1972). mostly emerged and have only their Some emergent aquatics, e.g., Mon short stems below water. Species of trichardia arborescens (L.) Schott, Pel Acorus, Anubias, Lagenandra, Spa tandra virginica (L.) Kunth, Cryptoco thiphyllum and especially Cryptocoryne ryne ciliata (Roxb.) Fischer ex. Schott are used as aquarium plants and may be (D. Nicolson, pers. comm.) and Typhon submerged completely for indefinite pe odorum lindleyanum Schott O. Bogner, riods of time without apparent injury. pers. comm.), occur in tidal zones. Even Dieffenbachia has been used in While most emergent aquatiC genera aquaria (D. Nicolson, pers. comm.) in the neotropics are well-rooted, terres The Asian tropics, in contrast to the trial plants, some are epilithic, such as a American tropics, have large numbers of rheophytic group of Anthurium (A. submerged aquatics, the most important andicola Liebm., A. sytsmae Croat, A. being the genus Cryptocoryne. Members rupicola Croat and A. antioquiense of this genus spend most of their lives in Engl.) and SpathiphyUum (S. quin shallow water, but typically flower at diuense Engl.), although the percentage periods of low water (when their leaves of rheophytic species for each genus is have emerged above water level) or low. when the water level is low Oacobson, The Asian tropics, on the other hand, 1980, 1982;). Bogner, pers. comm.). are much richer in rheophytic plants. Aridarum, Bucephalandra, Cryptoco 1.2 Free-floating Aquatics ryne, Furtadoa, Heteroaridarum, Hotta Free-floating aquatics are represented rum, Lagenandra, Phymatarum, Pipto- 6 AROIDEANA, Vol. 11, No.3 spatha, some Homalomena and some considered aquatiC in the true sense. Schismatoglottis, have the majority, or Many are, in fact, principally epiphytic all, of their species occurring along or in genera which find steep, well-drained streams, frequently clinging to rocks on stream banks good substitutes for the stream banks (van Steenis, 1981). normal epiphytic habit (see below). The majority of emergent aquatic plants are not rheophytic, but rather 2. Terrestrial Plants occur in flowing or standing water. The terrestrial habit is predominant Among the New World genera, which for aroids on a world-wide basis. Terres are nearly always found growing in trial genera are the most diverse ecologi water, are Dracontioides, Montrichar cally, occurring in humid to very dry dia and Urospatha. Other genera, such as habitats, in secluded forest understory Diejjenbachia, Philodendron and Spa and in open, exposed areas. While most thiphyllum have some species growing genera comprise mainly understory in aquatic or marshy situations. An plants in primary forest, some range into aphyllopsis (A. Hay, 1989) grows along savannas, exposed steppes, alpine mead streams or in swampy areas in the ows and even into semidesert areas. understory and survives partly underwa Terrestrial aroids range in habit from ter part of the year. Homalomena some caulescent plants (Diejjenbachia and times occurs in varzea forest in the Aglaonema) to tuberous plants (Amor Amazon basin, and survives underwater phophallus, Arum and Dracontium), to conditions for long periods, then toler rhizomatous (rarely also reported as ates swampy situations until the water cormose - see Colocasia, Therio fully recedes. phonum or 1jIphonium in Appendix II.) In addition to the rheophytic genera and to subscandent plants ( Cercestis and mentioned above, there are a number of Culcasia). other, chiefly emergent aquatics in Asia A large percentage of terrestrial aroids usually growing along streams or in have rhizomes, or short stems with short swamps. They differ in that they are not internodes, which usually creep over the usually clinging to rocks or to steep surface of the soil or just beneath the soil banks, but are rooted along the edges of surface. Rhizomes may be deeply rooted, water courses and usually have subterra as in Cyrtosperma and Spathiphyllum, nean root systems. These include most but most are weakly or loosely rooted. A species of Cryptocoryne, Cyrtosperma, few species of Anthurium (e.g., A. as well as Anubias, Aglaodorum (in ochranthum K Koch, A. pluricostatum brackish water), Lagenandra, Lasia and Croat & Baker) and Philodendron (e.g., Podolasia. P. grandipes K Krause) are deeply

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