4 AROIDEANA, Vol. 10, No.2 Morphological Variation in Aroids J. Bogner Menzinger Strasse 63 0-8000 Munich 19 West Germany INTRODUCTION The Araceae or aroid., are a large family or roasted (or otherwise heated) to of about 2400 species, grouped in 107 become edible. Essentially, plants have genera and these again in nine subfami­ produced poisons to protect themselves lies. The aroids are mainly a tropical from being eaten by animals. Several aroids family and are distributed world-wide. also have uses in folk-medicine. For in­ They show great variation in their mor­ stance, Acorus calamus has been used phological characters, which will be de­ since ancient times for stomach ailments. scribed in this paper along with some Tjlphonium blumei Nicolson & Sivadasan other data. is used to treat diarrhea in tropical Asia and was brought by man (probably from USES India) to Africa, Madagascar and to the Neotropics (Brazil, Venezuela), where it Many aroids are very handsome orna­ is naturalized today. The Indians in Co­ mental plants and often cultivated, to men­ lombia use Urospatha antisylleptica R. E. tion just a few: Monstera deliciosa Liebm., Schultes, Philodendron dyscarpium R. E. Dieffenbachia maculata (Ladd.) G. Don, Schultes and Anthurium tessmannii Krause Epipremnum aureum (Linden & Andre) for contraceptive purposes. Roots ofHeter­ Bunting, many Philodendron species etc. opsis spruceanum Schott are used for Monstera deliciosa also has a delicious basket-weaving and certain aroids as arrow fresh infructescence tasting like pineap­ poisons for hunting by indigenous people. ple. Others are important food plants, like These are just a few examples of the uses Colocasia esculenta (L) Schott, the Taro, of aroids, about which much more is in which the tuberous stems and the known. leaves are eaten cooked; Amorphophallus paeoniifolius (Oennst.) Nicolson is culti­ ECOLOGY vated for its starch-rich tubers in tropical Asia, mainly India. Cyrtosperma merkusii The aroid., are adapted to many habi­ (Hassk.) Schott var. chamissonis (Schott) tats and more than 90% are tropical. The A. Hay is grown in Southeast Asia and a majority prefer warm and humid condi­ few Xanthosoma species, originally from tions, but aroids have also conquered tropical America, are cultivated in the periodically dry areas, where they have a Neotropics, tropical Africa and Asia. Some resting period with dormant rhizomes, others are also used by indigenous people, tubers or very fleshy roots (Stylochiton). like seeds of Tjlphonodorum lindleyanum But nearly all of these prefer shady places, Schott in Madagascar and the roasted seeds at least under trees or shrubs or between of Montrichardia by Indians in tropical rocks. One, Zamioculcas, is a succulent South America. Many aroids are poison­ plant and stores the water in its thick ous in the fresh stage, including those petioles. Aroids also grow in very special mentioned above which are used as food ecological niches, like rheophytic habi­ plants (Colocasia, Xanthosoma, Cyrto­ tats; true rheophytes are Aridarum, sperma, Amorphophallus). Their stems, Bucephalandra, Piptospatha, etc. Others rhizomes, tubers or leaves must be cooked grow permanently submerged Qasarum, ]. Bogner, 1987 5 many Cryptocoryne species) or float on GROWTH FORMS the water surface (Pistia). Some aroids (Aglaodorum, several Cryptocoryne, e.g. Aroids have many different growth C. ciliata, tolerate brackish water and forms. Most are terrestrial plants growing occur in fresh water tidal zones in tropical in the soil or high climbers which can Asia). But no aroids occur in true deserts· become disconnected from the forest floor some grow in very dry areas (Arum and and then send down long feeding roots Eminium in Central Asia, Arum and Biarum to the soil (= hemiepiphytes). It can be in North Mrica and the Orient, Arisaema expected that all climbers exhibit skototro­ pism, but this has so far been proven for in the Arabian Peninsula and East Mrica a few Stylochiton species reaching th~ only a few species to date. There are also Sahel zone), but all of these areas have a true ep~phytes (many Anthurium species, Remusatia), swamp plants, true submerged certain rainy season each year, during aquatic plants Qasarum, most Cryptoco­ which they can grow vegetatively. Tem­ ryne species) and a free-floating species, perate areas are poor in aroids, but con­ Pistia stratiotes L. tainsome old isolated genera (Calla, Symplo­ carpus, Orontium, Lysichiton, all of which are swamp plants). Calla and Lysichiton MORPHOLOGY are distributed northwards to the subarc­ Vegetative Parts (shoots, vegetative tic zone (Calla to northern Scandinavia propagation) Lysichiton to Alaska). A few of the othe; mainly temperate genera (Arum, Arisaema, Aroids are herbaceous, perennial herbs, Pinellia) grow on the forest floor or at some very large, or subshrubby climbers least in shady places under trees or shrubs, with somewhat woody older stems. The but in all these cases their rhizomes or leaves are arranged in rosettes or the tubers are dormant during the cold season. internodes may be long, especially in the Some aroids go high up into the Andes root climbers, where some groups (Mon­ (Gorgonidium ca. 3000 m) or Mrican stereae, Cercestis) flagelliform shoots mountains (Arisaema ruwenzoricum up ( = flagelles), with very long internodes to 3200 m on the Ruwenzori), where a and cataphylls only, also occur. Some warm temperate climate exists. The high­ aroids have upright short stems with the est altitude is reached by the genus Ari­ leaves at their apex (Alocasia, Xantho­ saema in the Himalaya, where Arisaema soma sect. Xanthosoma), pseudostems (Ty­ lobatum Engler andAjacquemantii Blume phonodorum), creeping rhizomes or are growing up to an elevation of 4500 tubers; rarely they may be tree-like (Mon­ m, Arisaema flavum Schott up to 4400 m trichardia with stems up to 6 m, some and for some other species an altitude species of Xanthosoma with trunks to 3 up to 4000 m is reported. Some aroids m tall and some species of Alocasia such grow under semi-epilithic conditions, with as A portei Becc & Engl., A macron-hiza ~heir stems, rhizomes or tubers growing (L.) G. Don,A odora C. Koch). The ramifi­ 10 humus deposits in holes or crevices of cation of aroids is usually sympodial, rarely steep rocks (limestone hills in Malay pen­ monopodial (Potheae). Vegetative propa­ insula with Colocasia gigantea Hook. f., gation usually occurs. There are shoots, Amorphophallus; washed out holes in lime­ often specially formed as long runners stone in Madagascar with CarJephyton, (stolons) with a rosette of leaves (Crypto­ Colletogyne; or granitic hills in Eastern coryne) or a tuber at their apex (some Brazil with a few hard-leaved Anthurium Alocasia, few Amorphophallus). Some pro­ sI?ecies). The rheophytes grow mostly duce underground runners several metres directly on rocks under very humid con­ long (Lasiomorpha senegalensis Schott), ditions. quickly occupying large areas. The flag­ elles (with their very long internodes) of 6 AROIDEANA, Vo l. 10, No, 2 Fig, 1 AridclI'/llII nico/sollii Bogner, r\ t\-p ic li rheoph\Te gnw,ing o n sa ndstone rocks at Sllnga i Tamhak, ;\ It. Sa ntllhong, Sara\\'ak, J Bogner Fig. 2 Crl plocor)'ne /Jo illederiljolia Sc hott growing in a N lpaji'ulical/s swa mp nea r T~l b a ki s , S llm ~ ltr a , Incionesia,.J. Bogner fig, 3 Lagel/andra ol'a la (L.) Th\\'aites, in Sri Lanka (Ce\'lo n ), J. Bogner fig, -i Lasia COl7cilllla V ,A. \' R, This ve n ' ra re amid from Ka limantan, grmving in the Keb lll1 I ~a\'a, /3 ogor (.1<I\'a), \XI. Herrmann J. Bogner, 1987 7 several Monstereae and Cercestis enable stereae). There is often a great difference them to quickly reach another branch or between juvenile and adult leaves. In most tree. Peculiar erect or horizontal above­ cases, the first foliage leaf (of a seedling), ground shoots with many small bulbils is entire; subsequent leaves may become also occur in Remusatia and Gonatanthus. increasingly divided, sometimes ending One bulbil is produced on the upper part up highly compound; between the ex­ of each petiole in Pinellia temata Makino tremes, all intermediate leaf-forms exist. (synP. tuberifera Ten. and a few on the There are species, for instance in the leaf-blade of Amorphophallus bulbifer genera Syngonium and Xanthosoma, in (Roxb.) BI. Much more common are tu­ which juvenile and adult leaves are always bercles produced sometimes in large quan­ entire, yet other species in the two men­ tities around the apex of an old tuber tioned genera have compound (pedate) (Dracontium), or in lower numbers in leaves in the adult stage. But there are many other tuberous species (Arisaema, other genera, like Gonatopus and Amor­ JYphonium). Another unusual type ofvege­ phophallus, in which the first foliage leaf tative propagation is by broken leaflets, (of a seedling) is already divided; they in Zamioculcas and Gonatopus; the leaf­ never have entire leaves. lets fall down by a slight touch, then root Leaf venation in aroids is parallel or in the soil and form a tubercle from which reticulate, but in both types we can find a new leaf will develop. some variation in certain groups, like Pothos or Colocasioideae; also somewhat Leaves intermediate types exist, where the (pri­ mary) lateral veins of the first order are Aroid leaves show very great variation. parallel, but the lateral veins of the second The leaves are usually arranged spirally, order are reticulate (some Monstereae, only rarely distichously or solitarily (Am­ Spathiphyllum). One (or two) collecting orphophallus, Dracontium). The petiole veins running along the margin of the is usually well developed and has a sheath, leaf-blade are quite common, where the which protects the young, still furled leaf; lateral veins of the first order turn up­ only rarely are leaves subsessile.