Wood Anatomy of Selected Cucurbitaceae and Its Relationship to Habit and Systematics

Nord. J. Bot. — Section of structural botany Wood anatomy of selected Cucurbitaceae and its relationship to habit and systematics Sherwin Cariquist Cariquist, S. 1992. Wood anatomy of selectes Cucurbitaceae and its relationship to ISSN 0l07—055X. habit and systematics. — Nord. J. Bot. 12: 347—355. Copenhagen. Qualitive and quantitative data are presented on wood anatomy and cambial confor mations of four species of Cucurbitaceae. Although all woody to various degrees, the four species were selected to show a wide range of habits and therefore to discern possible correlations between habit and wood anatomy. Vessels are widely spaced and libriform fibers are minimal where storage of water and carbohydrates is promi nent. Axial parenchyma is dimorphic: lignified thick-walled paratracheal may lend strength to the vessel elements (which are wider than long), whereas thin-walled apotracheal parenchyma may lend flexibility to stems (especially in lianoid species) and serve for storage. Rays are multiseriate only and alter little from primary rays (but large multiseriate rays originate suddently in fascicular areas of one species). Distribution and abundance of libriform fibers relate to habit: most abundant in the shrubby Acanthosicyos, least in the storage-oriented lower stems of Apondanthera). Vasicentric tracheids extend radially and interconnect vessels, potentially providing a subsidiary conductive system that would maintain the conductive pathways of the large vessels if some of those vessels were to be disabled or deactivated. Cucurbita ceae are characterized by septate fibers, vasicentric tracheids, and storied wood structure. Each of these features is found in at least half of the families now commonly included in Violales, to which Cucurbitaceae are thought to belong. S. Cariquist, Rancho Santa Ana Botanic Garden and Dept of Biology, Pomona College, Claremont, California 91711, USA. Coccinia grandis J. A. Voigt is a rain forest liana al Introduction though with moderate woodiness (up to about 10 cm in are 5 cm in diame Cucurbitaceae are a family often thought to be non- diameter); the stems at my disposal vine in which only woody. Indeed, Metcalfe & Chalk (1950), who for most ter. Zanonia indica L. is a rain forest occurs in the families of dicotyledons devote a section to “wood” a limited amount of secondary growth imperforate omit such a section for Cucurbitaceae. There are, how vascular bundles. The features of vessels, ray parenchyma, ever, several Cucurbitaceae that become moderately tracheary elements, axial parenchyma, with respect to woody. Four of these have been selected because they and variant cambial types are analyzed Zimmermann’s represent divergent habits that may form the basis for habit of these four species. Although on Cucur correlations between habit and wood anatomy. Acan (1922) neglected but magnificent monograph information, the thosicyos horridus Weiw, is a shrub of Namibian sand bitaceae contains much anatomical needed characteriza dunes; the lower stem, usually buried beneath the sand, wood histology of the family has may develop a woody cylinder 1—2 cm in diameter. tion and analysis. is of interest with Apodanthera undulata A. Gray, from arid areas of New Wood anatomy of Cucurbitaceae placed Cucurbita Mexico, has a tuber-like storage root; the base of the respect to systematics. Older systems along a line stern forms a woody transition to this storage organ. ceae in an order such as Campanulales, Accepted 28—11—1991 © NORDIC JOURNAL OF BOTANY NORD J. BOT 12: 347—355 347 Nord. J. Bot. 12 (3) (1992) , . %1U !.1 cam i.. L -4 A tap il’c / • SAt •1 L..iii’ 4 Figs 1—4. Stem sections of Acanthosicyos horridus (Carlquist 8086).— Fig. 1. Transection, showing two zones of secondary phloem (plus a few libriform fibers) produced by a cambium abaxial to intraxylary phloem strands in the pith; at top, multiseriate rays begin abruptly in the two fascicular areas. — Fig. 2. Vascular strand formed by cambium abaxial to intraxylary phloem strand; vessels as well as libriform fibers are in the secondary xylem formed by this cambium. — Fig. 3. Transection of secondary xylem from main woody cylinder, to show perforated ray cells (traversing the ray, above and below), sclerified ray cells, and distributon of thin-walled axial parenchyma. — Fig. 4. Tangential section of wood from main woody cylinder; large multiseriate ray at right, portion of one left; storied nature of the thin-walled axial parenchyma evident. — Fig. 1, scale shown above Fig. I (finest divisions = 10 sm); Figs 2—4. — scale shown above Fig. 2 (divisions = 10 sm). Symbols: cam = cambium, If libriform fibers, sap = sclerified paratracheal axial parenchyma; sp = secondary phloem sx = secondary xylem: tap = thin-walled apotracheal axial parenchyma. a--- L_ transection of cambial region to Figs 5—8. Wood sections of Cucurbitaceae. — Fig. 5. Acanthosicyos horridus (Carlquist 8086). show contrast between cambium in ray area and in fascicular region; sciereids in ray, below. — Fig. 6. Apodanthera undulata (Fosberg 53738), portion of vessel wall from tangential section, to show wide grooves interconnecting pits apertures. — Figs 7—8. two pockets of secondary phloem Coccinia grandis (J. B. Fisher 88—23). — Fig. 7. Wood transection; ray cambia have produced along the fascicular area in which several vessels and associated libriform fibers are present. — Fig. 8. Tangential section; ray in 6 (divisions = 10 sm). — center; storying evident in axial parenchyma. — Figs 5, 7, 8, scale above Fig. 2; Fig. 6, scale above Fig. sap = sclerified paretracheal axial Symbols: cam = cambium in fascicular area; If libriform fibers; rc = cambium in ray area; parenchyma; sp = secondary phloem; tap = thin-walled axial parenchyma. __ ‘fr ;:‘ ;.-% j-: ii[ -— — Fig. 9—12. Wood sections of Cucurbitaceae. Figs 9—10. Apodanthera undulata (Fosberg 53738). — Fig. 9. Transection of wood from lower stem, showing vessels of a fascicular area with rays to the right and left of it. — Fig. 10. Portion of tangential section of wood, showing vessel wall (right), axial parenchyma to the left of the vessel wall, and, at left, two libriform fibers. — Figs. ll—12.Zanonia indica — (Hartley 10037). Fig. 11. Vascular strand with secondary xylem (large vessels) from transection of stem. — Fig. 12. Portions of vasicentric tracheids, showing large bordered pits, from tangential section of stem. — Figs 9, 11, scale above Fig. 2; Fig. 10, 12, scale above Fig. 1. leading to Asterales (e.g., Wettstein 1935). In more calculations do not readily reveal the nature of the recent systems, however, Cucurbitaceae is uniformly wood. Obviously, vessel density drops markedly in the placed in Violales (Cronquist 1981, 1988; Dahlgren highly parenchymatous stems and roots in which storage 1975, 1980; Takhtajan 1980; Thorne 1976, 1983). Be of carbohydrates and water is prominent. cause wood histology of Cucurbitaceae has not hitherto been summarized or analyzed, the ways in which wood features of the family may relate to systematics have not been hitherto presented. Anatomical descriptions Acanthosicyos horridus Secondary xylem produced by growth that increases the radial extent of the bundles of the primary stem as well Materials and methods as by cambial action adjacent to the strands of intraxyl Wood of Cucurbitaceae offers problems for sectioning ary phloem. Growth rings absent, although mild fluc in two respects: it is softer than most woods sectioned utation in diameter of vessels evident (Fig. 3). Vessels successfully on a sliding microtome, and the large ves mostly solitary (Figs 1, 3); mean number of vessels per sels are likely to fracture during sectioning on a sliding group, 1.32. Mean diameter of vessels, 128 Ism. Mean microtome. However, the wood of Cucurbitaceae is vessel element length, 89 sm. Mean vessel wall thick hard enough so that it cannot be sectioned successfully ness, 5.2 lAm. Perforation plates simple. Lateral wall by the ordinary paraffin methods that involve sectioning pitting of vessels alternate; pits 6—9 im in diameter. Pit with a rotary microtome. An ideal method that solves apertures elliptical or wider; when wider, forming these problems involves softening of the wood with grooves that interconnect pit apertures. Narrow vessels ethylene diamine, followed by embedding in paraffin and vasicentric tracheids, often with distorted shapes and sectioning on a rotary microtome (Carlquist 1982). that are variously rectangular in longitudinal section radi A very important element in this method is the soaking present, interconnecting vessels or vessel groups in water of exposed surfaces of paraffin-embedded ma ally. All other imperforate tracheary elements are sep terial prior to sectioning; sectioning of tissues that have tate libriform fibers with simple pit s. Mean libriform not been subjected to the soaking process is much less fiber length, 539 p.m. Mean libriform fiber diameter at effective. widest point, 32 p.m. Mean libriform fiber wall thick Sections were stained with safranin and fast green. ness, 5.2 p.m. Axial parenchyma of two types: para and Macerations were prepared by means of Jeffrey’s fluid tracheal thick-walled lignified cells (“sap” in Fig. 4) in and stained with safranin. thin-walled nonlignified cells that are clearly storied The material of Acanthosicyos horridus was collected tangential sections (“tap” in Fig. 3, 4). Paratracheal in Namibia in 1989, thanks to a grant from the Amer parenchyma cells distorted in shape by vessel enlarge ican Philosophical Society. Jack Fisher of the Fairchild ment; pits of paratracheal parenchyma cells bordered Tropical Garden kindly provided the material of Cocci (bordered pit pairs) facing vessels, but pits simple on nia grandis. Material of both of these species was fixed other walls. Thin walled axial parenchyma cells present in formalin acetic alcohol. Material of the two other as variously shaped bands or patches as seen in transec in species was dried, and was obtained from specimens in tion (Figs 3, 5), but fusiform or, less commonly, the herbarium of the Rancho Santa Ana Botanic Gar strands or two cells as seen in longitudinal section (Fig.

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