INTRODUCTION VEGETATIVE GROWTH AND (see below) to detail the shoot architectural patterns in MORPHOLOGY the family. Since then, the complex architectural habitsof this The Araceae occupy a relatively isolated position among family have been given improved descriptive tools by ¯owering plants due to their possession of a number of Ray (1986, 1987a,b,c). Ray (1987c) engaged the com- distinguishing vegetative and reproductive characters plexity of aroid shoot diversity and produced a scheme (MBB). Within the family a number of distinctive char- that allows structural comparisons across taxa support- acter states occur, especially in the larger or more basal ing evolutionary and systematic analyses. Beginning with genera, but few are diagnostic in themselves. It remains the whole shoot, the article (axis) is produced by the best to combine as many characters as possible when activity of a single meristem from origin to termination, making determinations. Particularly in the more derived abortion, or onset of sexuality. The shoot is a single genera, anatomical charactersare diminishedin variety (unbranched) article. The segment is an internode plus and must be combined with other morphological and associated leaf (or leaves) and bud. reproductive charactersfor thispurpose. In aroids, segments can be monopodial or branching, Growth form and habitat variety exceedsthat of any the latter being a junction between two articles. Ray other monocot family. The range includesvinesor large (1987b) investigated shoot organization, leaf types and herbs in tropical forests and borders, and plants with growth correlations of the segment. The two shoot types rhizomes or corms in seasonal dry or cold habitats (Bogner found in the Araceae are (1) monopodial, in which the 1987). Hemiepiphytesand epiphytesare not common but base of the petiole ensheaths the stem, and (2) sympodial occur in thirteen tropical genera (Benzing 1990). A useful where the shoot is continued after a foliage leaf by a bibliography, including anatomical citationsfor epiphytic sylleptic axillary bud; the shoot apex terminates by diff- species, can be found in Watson et al. (1987). Habitat ele- erentiating into an in¯orescence, and the petiole base does vation rangesfrom sealevel to greater than 3±4000 m. not encircle the stem. Plants with elongated stems are res- For a predominantly terrestrial family, aquatic adapta- tricted to taxa with predominantly monopodial segments. tions of several types are widespread. Steenis (1981, 1987) Ray examined the allometry among the componentsof and Cook (1999) have listed numerous observations on the segments and attempted correlations between parts. the family; together the lists include 29 genera distrib- His conclusions yielded no immediate systematic applic- uted among at least six subfamilies (including the four ation but have potential to contribute to understanding lemnoid genera), making 26% of the genera having the evolution of growth formsin the family. aquatic species. Most aroid aquatics are rooted plants Ray (1987c) studied shoot organizational diversity of with emergent stems and/or leaves. Some are submerged 83 species representing 27 genera and 20 tribes, plus (Cryptocoryne, Jasarum), or are rheophytes( Aridarum, Acorus. He noted that ¯owering isalwaysterminal in Bucephalandra, Piptospatha). Some prefer brackish aroids, and that sympodial and monopodial axes are dis- water (Aglaodorum and some Cryptocoryne). They may tinguished by whether or not the shoot is renewed after form rosettes (Anubias, Cryptocoryne, Jasarum), be free- ¯owering. After reviewing the early German and more ¯oating (Pistia) or planktonic (lemnoids). Cook pro- recent literature, Ray codi®ed terminology and revised posed that these adaptations have arisen independently Engler's diagrams that use a series of symbols to represent in the family many times. segment parts. They are useful in correlating structure Meusel (1951) reviewed the work by Engler (1877, and with phylogeny and systematics. His architectural analysis see Engler 1990 with translation by Ray and Renner) on of an unbranched system ®ts Chamberlain's Model in the the growth formsof aroidsand noted that sympodial system of Halle et al. (1978). Ray and Renner (in Engler growth isthe principal mode of extensionin genera with 1990) noted that leaf divergence (phyllotaxy) isgreatly elongated internodes, as illustrated by eight examples. in¯uenced by shoot diameter. Small shoots have a leaf Holttum (1955) supported these observations and called divergence approaching 1 : 2; larger diametersproduce a attention to the precision (exact number of leaves) of spiral arrangement. branch architecture in the climbing genera. Engler Leaf typeswithin the Araceae vary considerably devised the symbol and line diagrams later used by Ray (cf. Hay and Mabberly 1991) but were divided by 2 Introduction Ray (1987b) into four classes: those associated with (1) Hydrocharitaceae. However, ascurrently understood,it initiation of new shoots; (2) continuation axes; (3) resting would appear that she was describing the maturation of axes; and (4) termination and replacement of axes. The cells divided within the procambium. All tissue matures terms leaf, prophyll, mesophyll, bracteole, mesobracteole, at the xylem±phloem boundary asoriginally blocked out blastophyll, and cataphyll are used conventionally. When by the procambium; therefore, thisinterpretation of combined with modi®ers, such as foliar, ¯agellar, pro- the observation may not be credible. It is interesting that leptic, sylleptic, etc, the terms are de®ned and used in a the pattern of maturation she noted was also found in the much more precise way than before. Ray has provided apparently neighbouring Alismatales, which share a tools by which an evolutionary survey of shoot archi- similarvascularbundleconstruction(cf.Tomlinson1982). tecture of the family could be attempted. REPRODUCTIVE MORPHOLOGY Germination and growth The family is strikingly set off from other ¯owering plants The Araceae are found to produce a larger variety of by its signature feature, the in¯orescence. A terminal seedlingformsthanmostmonocotfamilies,variationwell- branch, the spadix, is subtended by a single leaf-like illustrated by Tillich (1985, 1995). In general, seedlings organ, the spathe. The spadix may be covered with closely are said to be endospermless, with reduced hypocotyl, packed bisexual ¯owers, or the plants may be monoecious having weak development of the cotyledonary sheath and with gynoecial ¯owers crowding the base of the spadix primary root. While Acorus seems easily excluded from the and androecial ¯owers formed distal to them. Distally, a Araceae, it appears we are not at all close to systematic sterile appendix may occur which may be variously col- use of seedling variation within the family. For that we oured. The spathe may be simple and re¯exed, or form an will need comparable stages and morphometric data on erect sheath, variously elaborated into a tube, and often relative expansion of mass of embryonic organs. Much of variously pigmented (MBB). the apparently marked variety in germinating embryosis probably due to heterochrony (cf. Gould 1977: 209 ff) In¯orescences and ¯owers and the variation might be organized using an approach that addresses this possibility. Flowers of the family are usually small and prism-shaped Shoot ontogeny of Calla wasstudiedby Scribailo and due to their packing geometry and usual unextended or Tomlinson (1992). The shoot apex was investigated by sessile form. Because of the inclusion of numerous crys- Hacciusand Lakshmanan(1966) in Pistia and Lemna. talsand/or mucilaginousmaterials,microtechnique Jaeger (1968) reported on vegetative growth in Remusatia. requiresunusualcare and patience. Therefore, detailed A study of meristematic activity of internodal meristems anatomical knowledge hasbeen slowin coming. Eyde in monocots(Fisherand French 1976, 1978) included et al. (1967) made the ®rst survey of ¯oral anatomy since several genera of Araceae. Both localized intercalary meri- Engler's period, where they described anatomy and vas- stems (interrupted) and uninterrupted internodal mer- culature of 18 genera. A series of detailed studies in ¯oral istems are found in the family. Anthurium (three species) vasculature were made by Barabe (1982, Symplocarpus; and Zantedeschia (one species) have uninterrupted meris- 1987, neoteny), Barabe and Chre tien (1985a, Spathicarpa; tems on reproductive axes as detected using surface 1985b, Monstera; 1986, Spathiphyllum), Barabe , Chre tien marking data. Aglaonema (one species) and Pistia stra- and Forget (1986, Anchomanes; 1987, gynoecia), Barabe tiotes have interrupted meristems on reproductive and and Forget (1987, Calloideae; 1988a, Zamioculcas; 1988b, vegetative axes, respectively. Spathiphyllum (three species) Aglaonema; 1992, Culcasia), Barabe , Forget and Chre tien has uninterrupted and interrupted meristems. No system- (1986, 1987, Symplocarpus), Barabe and Labrecque (1983, atic value can be imputed asyet. Calla; 1984, Lysichiton; 1985, Orontium), and Barabe , An intrafascicular cambium (as seen in TS) has been Labrecque and Chre tien (1984, Anthurium). Carvell's reported within vascular bundles of some Araceae (1989) large thesis also considered in detail ¯oral anatomy (Nicolas1916; Arber 1922a). Asdescribedby Arber, in of numerousgenera, emphasizingEngler'sPothoideae immature vascular bundles of Calla palustris and Arum and Monsteroideae. Its numerous detailed drawings of italicum,