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
Development, juvenile and adult Spathes stages The aroid spadix is subtended by a Cataphylls are leaves in which the blade modified leaf or bract, the so-called spathe. is not developed or is reduced, and in The spathe has undergone great modifi certain cases (stolons), all intermediates cations in its evolution, from an incon can be found, beginning with a minute spicuous green, leaf-like organ to a col blade at the apex of the cataphyll, and so ored, spreading and very showy one. The on. Cataphylls can be found on stolons, most highly specialized spathes are con flagelles, seedlings or on adult shoot.. in stricted between the female and male association with ramification. Cataphylls flowers or above the fertile flowers, with are usually membranaceous, though some a tube below and a showy lamina above. times weathering to fibers perSisting for But spathes may also be partly (Stylochi a long time on the stem (some Philoden ton, Sauromatum) or for most of their dron, Anthurium).; usually however they length marginally connate and forming a rot away qUickly, soon drying or falling kettle' enclosing the flowers (Lagenan off. Seedlings start with one or a few dra, Cryptocoryne). Usually the spathe is cataphylls before the first foliage leaf ap adnate below the spadix, but in two genera pears. Sympodial ramification terminates (Lysichiton, Orontium) the spathe goes in an inflorescence and the new shoot down to the rhizome and only encloses always starts with one or a few (depend (not adnate) the peduncle; this is an unique ing on the group) cataphylls. In several and, in my mind, another primitive char cases (Anthurium, Philodendron, Crypto acter. coryne) cataphylls appear but not inflo rescences, which are actually suppressed. But it is then easy to see that such a plant Flowers has already reached the adult stage, even Aroid flowers are nearly always sessile if juvenile and adult leaves are not differ (except shortly pedicelled in Pedicel ent. For example, if a Philodendron with larum), usually densely arranged on the uniform leaves (some have different leaf spadix and are always lacking a bract forms in the juverfile and adult stage) below each flower. Such bracts are always produces one foliage leaf after another present in the Liliiflorae, which are espe then it is in juvenile stage; if foliage leaves cially interesting in that they may imitate and cataphylls are produced alternately aroids in having densely flowered spikes then it is in the adult stage, but this does (Rohdea, Gonioscypha). The primitive not automatically mean that such a plant spadix in aroids is covered with perfect will produce inflorescenes. The length of flowers up to its apex. Then, an evolution the sheath also usually changes from the juvenile to the adult stage. ary tendency toward reduction of flowers appears. The upper flowers may become sterile and, in highly advanced spadices, we find a long terminal appendage with In.t1orescences out any sign of floral rudiments. Often The flowers of aroids are usually very sterile flowers appear between the male numberous and small, rarely few by re and female parts of the spadix, and these duction, and are generally arranged on a have a characteristic form in different fleshy axis, the spadix, only rarely in a groups. There is great variation among (non fleshy) spike (Pedicellarum, some sterile flowers, too. The female flowers Pothos). Not much is left of the spadix in are always situated on the lower part of the very reduced Pistia, and in the related the spadix, the male ones above them, Lemnaceae, the Duck Weed.. , the spadix except in Spathicarpa where male and is completely lacking. female flowers are arranged in longitudi- J Bogner, 1987 9 -
fig. ') Cn1JtoCOr l'lle ciliata ( I ~():\h.) SC hOll. shmYing the limh of spathe \yith :1 ciliate margin; from Celehes . J Bogner f ig. 6 AIII.1'drilIlJ/ blllJ/ile Schott, in tl O\y er from the ,\LtI:I\' Peninsuh J Ilogner rig. 7 rlllap/Jl'Ilopsis (//J/ eriC(//lCl (Eng !. ) A. H ~ I\ ' in tl O\ye r from rrench Gu\·ana. I Bogner rig. H Nobdea j (ljJOlliccl (Thunh.) A. \\'. I{oth r\ memher of the Li I iaceae first descrihed as an amid (Orolitillllljapollic/lJ/I ) Iw Thunherg. J Bogner 10 AROIDEANA, Vol. 10, No.2 nal rows with the spadix and spathe com structure, very thick and truncate (Anthu pletely connate. But in the related genus, rium, Dracontium, Urospatha) to mem Spathantheum, in which the spadix is also branaceous (Anadendrum, in which they entirely adnate to the spathe, the female are also shorter than the ovary and incon flowers are below and the male ones spicous). Tepals may either be free, partly above, as in typical aroids. The spadix in connate (some Pothos) or completely con other aroids is free, but in some genera nate and forming a cup (Pedicellarum, there is a partial adnation of the lower Spathiphyllum sect. Massowia, Holoch (female) part to the spathe. lamys). The number of tepals of the perigon The flowers themselves undergo a great in the genera Urospatha and Dracontium evolutionary reduction from perfect flow is inconstant. Urospatha sagittifolia (Rudge) ers to naked bisexual flowers to· naked Schott has flowers with four, sometimes unisexual flowers, with several intermedi five or six tepals as well as stamens on the ate forms. Plants with unisexual flowers same spadix. The same situation is found in the genus Dracontium, where up to are usually monoecious, but in Arisaema most species are paradioecious. Paradio eight tepals may occur and often the same ecious means that sexuality is not geneti number of stamens, though the latter may cally fixed, but depends on environmental have up to nine or twelve, and then do conditionsj stronger and bigger plants not correspond with the number of tepals. produce female flowers only, whereas This example shows that the question of weaker or younger plants produce male whether aroid flowers are basically di- or flowers only. Since the tubers are formed trimerous should not be overemphasized. anew in each vegetative period, it may happen that a small tuber is produced Unisexual flowers due to poor nutrients or the destruction of the leaf early in its growthj such a plant, Unisexual flowers with a well devel if it flowers at all, may produce male oped perigon are found in the genera flowers only. Arisaema species are nor Zamioculcas and Gonatopusj both have mallyeither monoecious or paradioecious, female flowers without rudiments of the but occasionally in certain usually paradi other sex, but the male flowers have a oecious species plants can be found with pistillode in the center. In Zamioculcas female and male flowers on the same the stamens are free, whereas in Gonato spadix. pus the stamens are connate with the fused filaments forming a ring around the As already mentioned, in the evolution pistillode. The unisexual flowers of Furta of aroids there has been an across-the doa are nakedj each male flowers consist') board trend toward reduction in flower of single stamen and one pistillode and structures. Perfect (bisexual) flowers with each female flower of a pistil with one a perigon become naked bisexual flowers staminode. Thccarum and Gorgonidium (Monstereae, Pycnospatha) or unisexual have male flowers with completely or flowers with or without a perigon, with panly connate stamens, but the central or without rudiments of the other sex. A pan of each synandrium is clearly of few examples should suffice to demon pistillodial origin. Most species of Sty strate thisj first, perfect flowers are con lochiton have a small, inconspicuous pis sidered. tillode in the center of the male flower, but their male flowers have free stamens Perfect flowers with filiform fiJaments and each male Perfect flowers in aroids usually have flower is surrounded by a saucer-like four or six tepals, in two whorls of two perigonj each female flower is surrounded or three, as well as the same number of by a cup-like perigon covering the whole stamens. The tepals are of a medium-thick ovary, and staminodes never present. The J. Bogner, 1987 11 flowers of the Arophyteae are naked and other characters, and the same can be said the very similar cup-like organ around in the ca..'ie of Zantedeschia aethiopica or the pistil of the female flower is clearly Amorphophallus cirrifer. At first, upon of staminodial origin, as it is proven by seeing A cirrifer with its long filiform the existence of bisexual flowers between staminodes around the pistils, one thinks the female and male flowers in some in terms of a separate genus, but a com species; other species have sterile flowers parison of other characters reveals that it ( = sterile male flowers) of the same struc is closely related to other species. I think ture in this region and form a so-called that this species is worthy of subgeneric synandrodium (lacking the anthers). A or sectional rank; Stapf, who described it, similar situation can be found in the genus has already established the subgenus Metan Asterostigma sea. Rhopalostigma, in which drium for Amorphophallus cirrifer. the staminodes around the pistil are con nate. Usually, the staminodes are free and surround the pistil; they are mostly four Staminodes or six in number, but there is some vari Generally, staminodes and sterile male ation. In the genus Homalomena there is flowers are quite variable in form, and usually only one staminode beside the both are used for cla..'isification. Stami pistil, or else staminodes are lacking alto nodes can be free or partly or completely gether. The staminode in Homalomena connate; their form varies from filiform, can be a..'i long as the pistil, in which case cylindrical, clavate or spathulate to scale It is often clavate, but in many cases it is like. These kinds of staminodes can sur much smaller and more or less conical round the pistils or lie between the female or conoidal or sometimes minute or com and male flowers, or above the male pletely lacking. Other examples are the flowers. Quite often synandrodia arise genera Zantedeschia and Amorphophal from connate staminodes or: from synan Ius. Zantedeschia aethiopica (1.) Spreng. dria, become steril, and are situated be has several staminodes around the pistil tween the female and male flowers or on of each female flower, wherea..'i all other the (apical) appendix. They are also vari species of this genus are completely lack able in form, often resembling the synan ing such staminodes. Another ca..'ie is Am dria, but without thecae and appearing orphophallus cirrifer Stapf, which has fili elongate or subrhombic in shape (viewed form staminodes around the pistil, all from above) and truncate in Caladieae. other species lacking any staminodes in Synandrodia in the Arophyteae are empty the female flowers. Some Amorphophal only in the center where there is usually Ius species have staminodes between the a pistil (in bisexual flowers, between the female and male flowers. Two species (A. female and male flowers). But synandro margaritiferus Kunth and A mysorensis dia can be also wart-like, flat, knob-like E. Barnes & c. E. C. Fischer) have peculiar or prismatic; these kinds are mostly found pearl-like organs in this position. Most on appendices. species of Amorphophallus have an (apical) appendix without any sign of staminodes, Male Flowers but a few unrelated species have an ap pendix with more or less well developed Male flowers are also distinctively staminodes. The conclusion is that the formed in the different groups. The male presence or absence of one or more flowers of Zamioculcas and Gonatopus staminodes, a..'i in the above mentioned have already been mentioned; these still examples, should be not overemphasized. retain a perigon. In other cases, male Those species of Homalomena without a flowers are naked. The stamens are free staminode in the female flower are closely or all partly or completely connate, and related to other species on the basis of then forming a synandrium. Free stamens 12 AROJDEANA, Vol. 10, No.2 may be in groups of two, three, four or six Pistils in a male flower, but they can also be solitary, which means that each male flower The aroid pistil usually has a slightly consists of only one stamen. The fila narrowed stylar region below the stigma, ments of the stamens may be filiform, but but long styles and sessile stigmas are also are more often flat. They may be fused known. The stigma is always wet and only basally or higher up, and there is covered with copious secretion during often much variation on the same spadix, the receptive phac;e, and dries afterwards. ac; in Gorgonidium mirabile Schott. But The stigma is capitate to disc-like, or mostly the filaments are completely con lobed to star-like, The ovary is unilocular nate and the thecae are arranged laterally to plurilocular, though unilocular ovaries or apically, or even marginally on the are pseudomonomerous, Two- or three synandrium. These synandria are mostly locular ovaries are common, and some truncate, but may be mushroom-like, cy species have ovaries with numerous 10- c1indric or of other shapes. Synandria can cules, There are one to many ovules per also be reduced to one stamen only (Col ovary or locule, in some species up to one letogyne). In Ariopsis, all male flowers hundred in an ovary. Great variation also are connate and form a single mass. exists in the type of placentation, Axile, parietal, apical, basal or bac;al and apical The anthers always consist of two thecae, placentation all occur in aroids. The ovules each of which consists of two pollen sacs. can be orthotropous, hemiorthotropous, The thecae open by means of a lateral slit or an apical pore or slit; the opening of amphitropous, hemianatropous or anatro pous. each pollen-sac separately is rare, Some (Cryptocoryne, Lagenandra, Aridarum) have horned thecae, ending in a more or less long tubule with poricidal dehiscence. The stamens of Aridarum are peculiar: the thick filament is excavated and the two Fruits thecae are situated inside or outside of the cavity, depending on the species. The fruits of aroids are usually berries with plenty of juice, rarely nearly juice less, closely packed in the infructescence, Generally, the berries are free, but form an indehiscent syncarp in Syngonium and, Pollen grains in Cryptocoryne, a syncarp which opens The pollen grains of aroids are of dif apically. The berries are usually indehis ferent types and their morphology is very cent (not opening), the ripe berries of useful for the classification of genera or Lagenandra open basally at maturity and higher taxa, The pollen grains are usually release the seed or seeds. Aroid berries shed in monads, but Xanthosoma and contain one to many seedc;. The spathe Chlorospatha have tetrads. The most primi can be deciduous after anthesis, drying tive aperture is the monosulcate type; a or rotting away, or may be completely or few genera have dicolpate (Calla, Rhaphido partly persistent, In many cases, the lower phora, Heteropsis), periporate (Anthu part of spathe (tube) protects the young rium), or extensive-sulcate or zonate developing fruits, then decays at maturity sulcate poll~n grains. Inaperturate pollen or actively opens (A1ocasia) to present the grains are, however, quite common. The colored berries, The berries in aroids are ornamentation of the exine also shows vividly orange to red or purple-red in great variation: smooth, rough, reticulate, color, white (many Philodendron species, foveolate, striate, echinulate (spiny), ver Stenospermation), sometimes green or rucose (warty), areolate and baculate, yellow (Typhonodorum), J. Bogner, 1987 13
Fig. 9 Po llen grain or Pislia slralioles L. \X '. BanhJo ll
Fig. 10 Po llen grain oJ' CO I/ClIOpUS /Joil'illii (Decne.) Hook. f. \V BanhJott
Fig. 11 Po llen grain of C)'JI I l/oslrlch)'s Cll/ceps R. Ik \'\'. 13anhlotl
Fig. 12 Po llen gr:lin or H(/jx t/il/e broll'llii I-look. f. \V Banhlott 14 AROIDEANA, Vol. 10, No.2
Seeds primarly attracted by smell, but also by the color and structure of the inflores Aroid seeds mayor may not have en cence (spathe and spadix). dosperm; some have only a little en dosperm, and there are all intermediates between plenty and no endosperm. The CHROMOSOMES embryo is mostly straight, though in some Chromosome numbers in aroid" are genera it is curved; it is usually not differ variable, and polyploidy occurs frequently. entiated, or rarely with a highly devel A primary base number of x = 7 can be oped plumula with several leaf primor estimated, but higher secondary basic num dia. Seeds with a highly developed plumula bers must be accepted. The highest number of the embryo always lack endosperm. known is well over one hundred chromo The outer integument is usually fleshy. somes. Some groups have a certain char The testa can be smooth, rough, ver acteristic number, sometimes a doubling rucose or striate. Genera with a highly of the genome; others have quite differ developed embryo (Nephthytis, Gonato ent numbers even within a single genus, pus) have a thin papery testa, but such where aneuploidy may occur (Cryptoco large embryos already contain chloro ryne). phyll. PHYLOGENY DISPERSAL OF SEEDS A personal conclusion about aroid phy The dispersal of aroid fruits appears to logeny must be allowed, without discuss be done mostly by birds (ornithochory). ing this in detail. In my opinion the ances Often the mature berries stay fresh for a tors of the aroid" must be sought in an old relatively long time (Arum, Nephthytis), group near the Liliiflorae, but not among just 'waiting for their dispersers.' Many recent species. Unfortunately the known aroid fruits (Philodendron, Dieffenbachia, fossil record" of both groups do not help Syngonium) are markedly ephemeral, dis in this matter. The idea of an origin of the appearing almost as soon a" they are aroids in the Liliiflorae is not new; several exposed. Dispersal by water is known authors (Hallier, 1912; Bessey 1915; Hutch (Montrichardia, Lagenandra, Cryptocoryne, inson, 1934, 1959; Novak, 1954; Kimura, Pistia) a" well a" by bat" (Xanthosoma 1956; Takhtajan, 1959) have suggested it. robustum Schott, maybe others). The seeds Engler (1920, p.47) briefly expressed a of aroids do not remain viable for a long similar opinion. Hutchinson (1934) hy time, and therefore long-distance trans pothesized that the aroids could be de port by natural vectors is probably not rived directly "from the stock of tribe possible. A"pidistreae of Liliaceae, in which the flowers are arranged in dense spikes (Tu POLLINATION pistra, Rohdea, Gonioscypha)." In my mind, there has certainly been convergent evo The flowers of aroid" are entomophilous. lution in this group toward an aroid-Iike The pollinators are mostly Diptera or habit. Coleoptera, in a few genera also Hymeno An interesting question is what would ptera (euglossine bees in Spathiphyllum). the ancestral aroid have looked like, and The flowers are proterogynous which what ancestral characters would it have favors a cross-pollination. Receptive stig combined? The very small flowers must mas and ripe anthers can overlap on one have had two whorls of three free tepals, spadix (Lysichiton americanus Hulten & two whorls of three free stamens and a St. John, some Anthurium). Apomyxis ha" superior, three-locular ovary. These flow only rarely been reported, but is probably ers must have lacked any bract below more common than believed. Insects are each flower; the flowers could have been ]. Bogner, 1987 15 laxly or densely arranged on a spike (not Ovule: the organ which develops after necessarily a "fleshy" flower axis or fertilization into a seed. An orthotropous spadix). They must have had an incon ovule has a straight axis with the hilum spicuous spathe (bract) below the flower and micropyle on the 0pp0.liite ends; an axis (spike), somewhat like a foliage leaf anatropous ovule is reversed, with the and not distinctively colored or formed. micropyle close to the side of the hilum. The venation type of the leaves could Perigon: a perianth consisting of equal have been either reticulate or parallel. parts, these called tepals (not differenti The leaf-blade must have been well devel ated into calyx and corolla). oped (the ensiform leaves of Acorus and Pistil: the female organ of a flower, con Gymnostachys could have evolved via sisting of ovary, style and stigma. neoteny). These hypothetical ancestral plants must not have been climbing (like Pistillode: a sterile (rudimentary) pistil. today's Pedicellarum or Pothos), but prob Placentation: the disposition of the pla ably had short, upright stems. Other primi centa or placentae. (Placenta: the organ tive characters must have been present, which bears the ovules in an ovary). such as monosulcate pollen grains and Pseudomonomerous: an unilocular endospermous seeds. Of course, we cannot ovary that originates evolutionarily from expect to find such an ancestral aroid still an ovary with more than one carpel. living today, but neverthelesss several Pseudostem: a false stem formed by aroid" have retained one or a few such overlapping sheathed petioles only; typi primnitive characters. Such ancestral plants cal example banana. may have existed for only a short geologi Rheophyte: flood-resistant plant grow cal period, died out quickly and were ing in and along swift running streams or succeeded by better adapted ones. rivers up to flood-level. EXPLANATION OF SOME BOTANICAL Skototropism: an orientation movement TERMS towards a dark area. The seedlings of certain climbers grow towards darkness, Anther: the apical fertile portion of a which in forest is nearly always a tree stamen, conSisting of two thecae, con trunk. nected by the connective, and each theca with two pollensacs (exceptions from this Stamen(s): the maleorgan(s) ofaflower. basic structure are rare.) The anthers con Staminode: a sterile or abortive stamen tain the pollen. (without an anther). Appendix: sterile terminal part of spadix. Synandrium: the stamens of a male Cultivar: variety originated in cultivation flower that are all connate. by selection, crossing or mutation. Synandrodium:structure formed bystami Epllithic (Semlepllithic): growing on nodes that are connate or a synandrium rocks (like some rheophytes); semiepil that becomes sterile (lacking the anthers). ithic: growing on rocks covered with Syncarp: a multiple or fleshy aggregate mosses etc., or very little humus. fruit-like structure formed of numerous Epiphyte: a plant which grows on other small fruits that are themselves connate; plants, but not parasitically. typical examples are pineapple or mul Geniculum: a knee-like, thickened joint berry. in the petiole, usually at the apex. Inflorescence: the disposition of the Tepals: units of a perigon. flowers on the floral axis. Testa: seed-coat. Integument: the envelope of an ovule. Theca: an anther half. Ovary: that part of pistil which contains Trichome: hair or any hair-like outgrowth the ovules. of the epidermis. 16 AROIDEANA, Vol. 10, No.2
ClTATED AND RECOMMENDED general part (par generalis) in Heft LITERATURE 74, the latter published 1920 (con tains the reference "Engler (1920, p. Dahlgren, R. M. T, Clifford, F. T, Yeo, P. 47"). F. 1985: The Families of the Mono Hutchinson,]. 1934: The Families ofFlow cotyledons. - Berlin, Heidelberg, ering Plants, II . Monocotyledons. - New York, Tokyo: Springer London: Macmil lan & Co. Ltd. Engler, A., in part with Krause, K., 1905- Takhtajan, A. 1959: Die Evolution der Angi 1920: Araceae. - In A. Engler, Das ospermen. - l ena: VEB Gustav Fisher. Pflanzenreich IV 23-A-F (Heft 21, 37, This book-contains a comprehensive 48,55,60, 64,71,73,74). - Leipzig: treatment of the evolution and phylo Engelmann. This monograph contains geny of fl owering plant,> and gives a also a comprehensive morphology large reference for the literature (see of the different subfamilies and in its there for further reference).
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