Vascular Patterns in Stems of Araceae: Subfamily Pothoideae Author(s): J. C. French and P. B. Tomlinson Source: American Journal of Botany, Vol. 68, No. 5 (May - Jun., 1981), pp. 713-729 Published by: Botanical Society of America Stable URL: http://www.jstor.org/stable/2442799 . Accessed: 19/08/2011 13:12 Your use of the JSTOR archive indicates your acceptance of the Terms & Conditions of Use, available at . http://www.jstor.org/page/info/about/policies/terms.jsp JSTOR is a not-for-profit service that helps scholars, researchers, and students discover, use, and build upon a wide range of content in a trusted digital archive. We use information technology and tools to increase productivity and facilitate new forms of scholarship. For more information about JSTOR, please contact [email protected]. Botanical Society of America is collaborating with JSTOR to digitize, preserve and extend access to American Journal of Botany. http://www.jstor.org Amer. J. Bot. 68(5): 713-729. 1981. VASCULAR PATTERNS IN STEMS OF ARACEAE: SUBFAMILY POTHOIDEAE1 J. C. FRENCH2 AND P. B. TOMLINSON Fairchild Tropical Garden, Miami, Florida 33156; and Harvard Forest, Petersham, Massachusetts 01366 ABSTRACT The stem vasculature of representative species of ten of the 11 genera in the Pothoideae was analyzed with the aid of films of series of transverse sections. In all species a leaf trace typically diverges from a continuing axial bundle before departing to a leaf, with the possible exception of Heteropsis. However, within this common organizational scheme a considerable range of variation exists, e.g., with respect to degree of branching of axial bundles, and distance from a leaf-trace branch to the point of leaf-trace departure to a leaf. In addition, we have found a wide variety of patterns of bud-trace organization in different genera of the Pothoideae. For example, prominent arcs composed of numerous bud traces occur in the central cylinder of Pothos, Pothoidium, and Heteropsis. Comparative anatomy leads to the conclusion that Pothos and Pothoidium more closely resemble Heteropsis than Anadendrum. Anadendrum should be dissociated from the tribe Pothoeae. With respect to other genera in the Pothoideae, our preliminary results suggest that each of the genera Anthurium, Culcasia, Zamioculcas, Acorus, and Gymnostachys are highly distinct from each other. VAN TIEGHEM (1867) published the only com- dans (Zimmermann, Tomlinson, and LeClaire, parative study of the organization and distri- 1974); 3) the usefulness of systematic compar- bution of stem vascular bundles in the Araceae. isons of vasculature in understanding evolution He observed that aroid stems could contain of the Araceae, and 4) the usefulness of stem either "simple" vascular bundles (i.e., with a vasculature as a primary diagnostic character single strand of xylem and phloem) or "com- in the Araceae. pound" bundles (i.e., with two or more dis- In this paper we are concerned with repre- crete strands of xylem and phloem that remain sentation of Engler's subfamily Pothoideae in distinct for considerable distances). The pres- which are included many distantly related gen- ent paper is the second of a series of reports era that lack both trichosclereids (some ex- on our survey of the vascular organization of ceptional species of Pothos have them) and the Araceae, which began with a description laticifers. The subfamily includes 11 genera of our approach and preliminary observations currently grouped in six tribes. Most genera (French and Tomlinson, 1980). Our prin- have: 1) bisexual flowers, except for Culcasia, cipal goals are to determine: 1) the extent to Gonatopus and Zamioculcas, which are uni- which the course of simple vascular bundles sexual, and 2) a perianth, except for Culcasia in aroids follows the pattern typical of palms and Heteropsis which have naked flowers. and other monocotyledons; 2) the extent to which the three-dimensional organization of METHODS-Table 1 lists the species exam- compound vascular bundles in aroids resem- ined and location of voucher specimens. Trans- bles the pattern recently worked out for pan- verse sections (T.S.) were made from either fixed or living stems using a Reichert OME sliding microtome fitted with a special clamp ' Received for publication 12 May 1980; revision ac- to accommodate long stem pieces (Tomlinson, cepted 25 June 1980. 2 Present address: Department of Biological Sciences, 1970; Zimmermann, 1976). Depending on in- Mississippi State University, Mississippi State, Mississip- ternode length, every section or sections at pi 39762. various regular intervals were kept for pro- We gratefully acknowledge material supplied by Josef cessing. In nonfleshy stems the average section Bogner (Munich Botanic Garden), Simon Mayo (Royal Botanic Gardens, Kew), Michael Madison (Marie Selby thickness in different species ranged from 60- Botanical Gardens, Sarasota), Marie-Francoise Prevost 130 ,um and up to 250 ,um in fleshy stems. (Center O.R.S.T.O.M., Cayenne, French Guiana), and Sections were cleared in 10% Clorox and con- Margaret Howard (University of Massachusetts, Am- centrated HCl, stained in basic fuchsin, mount- herst). We thank Keith Clancy for his careful technical with a assistance and Karen Esserchick for preparing Fig. 24-32. ed in Karo syrup; and photographed The critical review by Norman H. Boke is appreciated. Bolex 16-mm movie camera mounted on a Research supported by Grant DEB 77-07237 from NSF. stand above a Wild M20 microscope. The sec- 713 714 AMERICAN JOURNAL OF BOTANY [Vol. 68 tions were oriented for photography by means Internode T.S. (Fig. 1): The cortex is wide of outline drawings of bundles made with a and relatively undifferentiated but with a well- camera lucida attachment (Zimmermann and developed system of over 100 vascular bun- Tomlinson, 1966), and two frames were ex- dles, each with a well-developed continuous posed per section. Films were projected for sclerenchymatous sheath. Each larger cortical analysis with an L-W 224 A Photo Optical Data bundle has a single wide metaxylem element Analyzer, permitting variable speed frame-by- and a narrow phloem strand. There is no en- frame analysis. Plots of bundle pathways were dodermis, but the central cylinder is delimited made from measurements of relative bundle abruptly by a broad sclerotic layer, gradually distance from the center of the stem against transitional to the thinner-walled, unlignified position along its length. In the subsequent central ground parenchyma. Most vascular description, the courses of vascular bundles bundles in the crowded peripheral region have are followed basipetally, i.e., from the appen- a single wide metaxylem element and a con- dage (leaf or branch) into the main axis. This spicuous phloem strand, but they alternate is purely a descriptive convention and obvious- with a few much narrower ones. Evidently, ly does not refer to the generally acropetal many of the central bundles are recently in- method of development of the vascular system. serted leaf traces that have a poorly differen- The limitations of our present method of pre- tiated sclerenchymatous bundle sheath and sentation should be made clear; the plots refer well-developed narrow protoxylem elements. to a few selected, representative vascular bun- Closer to the nodes there may be occasional dles from the total system presented in the small bundles, usually the distal ends of branch analytical movies. For this reason we have also traces. presented gross analytical diagrams which con- Node T.S. (Fig. 3): In a single section in the vey some of the overall structural impressions nodal region the most conspicuous feature is obtained from the analyses. In labeling the the broad arc of branch-trace tissue which pen- plots of bundles (Fig. 33-41) after fusion of a etrates deeply into the central cylinder. Most leaf trace (open circle) and axial bundle (closed of the branch-trace elements are undifferen- circle) an intermediate symbol (half open) is tiated vascular bundles, although the proximal used for the next few points. The point at which extension can be recognized as discrete traces. the half circle is changed back to full is arbi- Laterally, anastomosing between cortical bun- trary and meant only to suggest that anatomical dles is also evident. At a restricted level im- changes, such as the loss of protoxylem, are mediately below the node there are 6-8 ad- observed as a leaf trace is integrated into the ventitious root traces, each of which is inserted vascular system of the central cylinder. opposite lateral leaf traces (e.g., Fig. 27). Course of the vascular bundles, (a) node. RESULTS-Morphology-Species we ex- (Fig. 24-27): Within the stem, the leaf-trace amined from six of the genera-Pothos, Po- system consists of an arc of about ten wide thoidium, Anadendrum, Heteropsis, Culcasia, bundles, each of which continues into the cen- and Anthurium-are vines climbing by means tral cylinder. The central bundle is a conspic- of roots ("root-climbing vines"), and four are uous median trace (Fig. 3). A larger number rhizomatous-Gonatopus, Zamioculcas, of narrow leaf traces enter and remain confined Gymnostachys, and Acorus. Phyllotaxis is dis- to the cortex. tichous in Pothos, Pothoidium, Anadendrum, The cortical system remains discrete, but Heteropsis, Culcasia, Acorus, and Gymno- there is anastomosing between cortical bun- stachys, but spiral in the species of Anthurium dles, beginning first just above the node, i.e., we examined. Zamioculcas has a pattern of immediately above the axillary bud. This is leaf distribution with alternate scale and foliage initially recognizable by displacement of those leaves, in which the leaves are essentially spi- cortical bundles in the path of the entering leaf rodistichous (Engler and Krause, 1905-1920). trace (Fig. 24). These bundles are displaced in The morphology of Gonatopus marattioides a tangential direction, and anastomose freely has not been described in detail (see fig. 4 in with other bundles.