PRESENCE OF VESSELS IN WOOD OF SARCANDRA (CHLORANTHACEAE). COMMENTS ON VESSEL ORIGINS IN ANGIOSPERMS

PRESENCE OF VESSELS IN WOOD OF SARCANDRA (CHLORANTHACEAE). COMMENTS ON VESSEL ORIGINS IN ANGIOSPERMS SHERWIN CARLOI Re; ;. Inc.

Amer. J. Bot. 74(12): 1765-1771. 1987. PRESENCE OF VESSELS IN WOOD OF SARCANDRA (CHLORANTHACEAE); COMMENTS ON VESSEL ORIGINS IN ANGIOSPERMS 1 SHERWIN CARLQUIST Rancho Santa Ana Botanic Garden and Department of Biology. Pomona College. Claremont, California 91711 ABSTRACT Sarcandra is the only genus of Chloranthaceae hitherto thought to be vesselless. Study of liquid-preserved material of 5. glabra revealed that in root secondary xylem some tracheary elements are wider in diameter and have markedly scalariform end walls combined with circular pits on lateral walls. Examination of these wider tracheary elements with scanning electron microscope (SEM) demonstrated various degrees of pit membrane absence in the end walls. Commonly a few threadlike fibrils traverse the pits (perforations): these as well as intact nature of pit membranes in pits at ends of some perforation plates are evidence that lack of pit membranes does not result from damage during processing. Some perforations lack any remnants of pit membranes. Although perforation plates and therefore vessels are present in Sarcandra roots, no perforations were observed in tracheary elements of stems or lignotubers. Further, stem tracheids do not have the prominently scalariform end walls that the vessel elements in roots do. Presence of vessels in Sarcandra removes at least one (probably several) hypothetical events of vessel origin that m ust be postulated to account for known patterns of vessel distribution in angiosperms, assuming that they are primitively vesselless. Seven (perhaps fewer) vessel origin events in angiosperms could account for these patterns: two of those events (Nelumbo and monocotyledons) are different from the others in nature. Widely accepted data on trends of vessel specialization in woody dicotyledons yield an unappreciated implication: vessel specialization has happened in a highly polyphyletic manner in dicotyledons, and therefore multiple vessel origins represent a logical extension backward in time. If a group of vesselless dictyoledons ancestral to other angiosperms existed, they can be hypothesized to have had a relatively homogeneous floral plan now that Sarcandra-hke plants no longer need be imagined within that group. Sarcandra and other Chloranthaceae show that the borderline between vessel absence and presence is less sharp than generally appreciated. THE WIDELY-CITED REPORT by Swamy and Bailey (1950) of vessellessness in wood of Sarcandra is of interest because Chloranthaceae have thereby been considered one of five families of woody dicotyledons to be primitively vesselless according to the concept of Thompson and Bailey (1916). The other families are Amborellaceae (Bailey and Swamy. 1948). Tetracentraceae. Trochodendraceae. and Winteraceae (Eichler, 1864; Harms. 1897; Tieghem, 1900). Chloranthaceae have been unique among the five families because only a single genus (Sarcandra) was presumed to lack vessels although the other genera of the family have them. Thus, if woody dicotyledons are primitively vesselless, we would have to assume that in Chloranthaceae Sarcandra represents a primitive condition, at least with re- 1 Received for publication 9 January 1987; revision accepted 1 1 March 1987. Appreciation is expressed to Drs. Vernon I. Cheadle. James A. Doyle. M. F. Moseley. and William L. Stern for reading the manuscript and offering helpful suggestions. spect to vessellessness and probably other characters as well. If vessels were absent in Sarcandra we would actually have, preserved in an extant family, the threshhold between vessel absence and presence; there would be an irony, though, in that Sarcandra does not appear to be particularly close to the other four families, all genera of which are vesselless. The report of vessellessness in Sarcandra by Swamy and Bailey (1950) has not been questioned, although the report was based only upon examination of stem material. The implications of a conclusion based on such limited material have therefore not been realized. We know that in some monocotyledons and in certain ferns (e.g., Marsi/ea), vessels may occur in roots only, with tracheids exclusively present elsewhere in the plant body (Cheadle, 1943; White. 1961). These groups are pertinent because Sarcandra. even though it has been called woody, is a small shrub the stems of which are a series of innovations of a few years' duration that arise from a condensed lignotuber-like rhizome a habit with resemblances to habits of 1765

1766 AMERICAN JOURNAL OF BOTANY [Vol. 74 monocotyledons, although different in presence of limited secondary growth. The stems do not. in my experience, have a xylem cylinder greater than 3 mm in thickness. The cambial activity at stem bases is moderate, and the term "lignotuber" may exaggerate the extent of this activity. The genus Chloranthus is less woody than Sarcandra to varying degrees, and stems in some species of Chloranthus are actually annual. Thus, differential organographic distribution of vessels, as in monocotyledons, does not seem improbable in the less woody Chloranthaceae. This is unlikely in Amborella, in which stems are multiple from a base, because the stems last for many years. Tetracentron, Trochodendwn, and most Winteraceae are trees; those species of Winteraceae that are not trees are shrubs with woody trunks rather than short-lived innovations from an underground base. Even though Sarcandra as well as other Chloranthaceae must be regarded as having vessels, the family nevertheless presents many very primitive xylary characteristics, and probably illustrates early stages in vessel evolution (e.g., perforations well bordered, pit membrane vestiges retained in perforations). Because Chloranthaceae demonstrate so many primitive features. I am extending the present study with a detailed survey of wood features in the family. This survey will include an SEM investigation of xylem of all species studies. MATERIALS AND METHODS The availability of liquid-preserved material of Sarcandra glabra (Thunb.) Nakai permitted this study. I collected this material on the upper slopes of Ishigaki Island, Ryukyu Islands, in 1982. I am particularly grateful to Dr. Mikio Ono of the Makino Herbarium, Tokyo Metropolitan University, for his help during these travels, which were made possible by a grant from the Japan Society for the Promotion of Science. Portions of stems, lignotubcrs. and roots from the collection Carlquist 15680 (RSA) were sectioned on a sliding microtome. Most of the sections were stained with a safranin-fast green combination. With sufficient intensity of staining by fast green, presence of pit membranes can often be revealed, but this is not a reliable indication of pit membrane presence. Because SEM can establish pit membrane presence with certainty, some sections were set aside without staining, and treated by the usual methods preparatory to examining them with ISI WB-6 SEM at the Rancho Santa Ana Botanic Garden. Macerations of stems, lignotubers. and roots were prepared by means of Jeffrey's Fluid and stained with safranin. Because the goal of this study was only to determine presence or absence of genuine perforations in various organs of Sarcandra, a thoroughgoing analysis of xylem variations in the genus was not undertaken at this time. Such analysis will be incorporated in the survey of wood anatomy Chloranthaceae presently in progress. RESULTS Study of sections of Sarcandra stem wood by means of light miscroscopy revealed the same uniformity reported by Swamy and Bailey (1950): all tracheary elements appear to be tracheids that differ from each other only to a small degree in diameter, a variation related to growth rings (Fig. 1). In radial sections of stems, one can see that overlap areas of tracheids are composed of circular to slightly elliptical bordered pits only slightly or not at all different from those on lateral walls (Fig. 2). Sections of root wood viewed by light microscopy (Fig. 3-5), show marked differences among tracheary elements. Transections (Fig. 3) show weakly-defined growth rings. Tracheary elements are much larger in diameter at some places in earlywood. If one views transections carefully, one sees that these wide tracheary elements are not restricted to earlywood; they may be found scattered in various places in areas of axial secondary xylem, and sometimes occur in short radial rows (Fig. 4). Examination of radial sections reveals that the wide tracheary elements have prominent scalariform patterns on end walls (= overlap areas), although lateral walls have scattered circular bordered pits. Because these wider tracheary elements look very much like vessels in diameter and end wall patterns, study of end walls by means of SEM to determine degree of pit membrane presence in the end walls is necessary. Investigation of radial sections of stems and lignotubers of S. glabra by means of SEM was also undertaken. Lignotuber wood has some tracheary elements that have wider diameters and scalariform end walls, but these cells are not readily analyzed under the light microscope because of their sinuous conformations. Examination of radial sections of roots with SEM (Fig. 6-10) reveals various degrees of pit membrane presence in the scalariform end walls. Some end walls appear to have few or no remnants of pit membranes (Fig. 6). Careful analysis of some of these end walls shows that only threadlike vestiges of pit membranes are present (Fig. 7). Other end walls show threads traversing the pit (perforation) areas (Fig. 8). The traversing threads as shown in Fig. 8 are important not merely to show that only ves-

Fig. 1-5. Wood sections of Sarcandra glabra, Carlquist 15860. 1. 2. Sections from near base of stem. 1. Transection, end of growth ring one-third from top of photograph. 2. Radial section, showing circular to shortly elliptical pits in tracheids. 3-5. Sections from root. 3. Transection, showing growth rings and wide rays. 4. Transection, showing tracheary elements with a range of diameters. 5. Radial section, showing the scalariform pattern of an overlap area of a tracheary element. Figure 1, 2. 4, 5, magnification scale above Fig. 1 (divisions = 10 /xm). Figure 3, scale above Fig. 3 (divisions = 10 Mm).

1768 AMERICAN JOURNAL OF BOTANY [Vol. 74 Fig. 6-10. Scanning electron photographs of portions of a single radial section of root wood of Sarcandra glabra. Carlquist 15680. 6. About % of the length of a perforation plate. 7. Four perforations from plates shown in Fig. 6. illustrating vestigial threads of primary' walls at margins of perforations. 8. Perforations from a perforation plate in which threadlike vestiges of the pit membrane traverse the perforations. 9. Pits from a scalanform end wall of a

December 1987] CARLQUIST WOOD OF SARCANDRA 1769 tiges of pit membranes are present, but also to show that artifacts have not been induced, since vestigial threads would likely be broken if pit membranes were damaged to any appreciable extent. Figures 9 and 10 show intact pit membranes in scalariform end walls. These membranes, like the threadlike vestiges, show little or no fracturing and also indicate that the degree of damage or artifact induction is minimal. In this connection, one should note that Fig. 6-10 were intentionally selected from a single wood section in order that any artifact formation would be much the same, whereas one could not certify that comparability if pit membranes from different sections had been photographed. Probably all of the pit membrane conditions in Fig. 6-10 represent artifact-free expressions. DISCUSSION The presence of vestigial threadlike fibrils traversing a perforation has been reported and illustrated by SEM by Meylan and Butterfield (1978) for Carpodetus serratus J. R. & G. Forster, Quintinia acutifolia Kirk, Q. serrata A. Cunn., Weinmannia racemosa L. F., and W. silvicola Sol. ex A. Cunn. A similar situation is illustrated by Meylan and Butterfield for Ascarina lucida Hook. f. (Chloranthaceae), although the microfibrillar webs they report are rather like those shown in Fig. 10 here than like those they illustrate for Cunoniaceae; the latter are like the threads shown here in Fig. 8. Meylan and Butterfield (1978) make it clear in their terminology that presence of a few threads, such as shown here in Fig. 8. does not qualify as a pit membrane and thus perforations are still present. Light microscope and SEM observations on stem wood perforation plates of Hedyosmum nutans Sw. demonstrate presence of coarse webs of pit membrane material in perforations of some vessel element end walls (original observation). Some perforation plates in Geissoloma marginatum (L.) A. Juss. studied by SEM show retention of pit membranes (Fagerlind and Dunbar. 1973). Very likely, as more primitive woods are studied with SEM, more pit membranes that indicate intermediacy between tracheids and vessel elements will be reported. These conditions illustrate that the transition between tracheids and vessel elements is not a sudden one; that we mav find these transitions in families of woody dicotyledons with numerous primitive features is not surprising (Carlquist, 1983). Clearly, Sarcandra has attained vessels in its roots, however. Thierry (1912) claimed vessels for Sarcandra glabra (as Chloranthus brachystachys Blume), but he obviously did not use the term in the same sense we do today; he was apparently referring to metaxylem tracheids with scalariformly pitted end walls in Sarcandra stems. For similar reasons, semidiagrammatic drawings of "Chloranthus brachystachys'"' stems that appear to show vessels (Thierry. 1912, pi. IV) can be discounted. Swamy and Bailey (1950) did not cite Thierry's work, so they did not contrast their claim of vessellessness in Sarcandra with Thierry's apparently imprecise observations and terminology. Thierry's camera lucida drawings do appear accurate, and his contention that Ascarina polystachya Forst. stems are essentially "coniferous" (e.g., have only tracheids) should be reinvestigated. These stems may have been too young to show vessel presence; vessels may appear tardily in ontogeny (Bailey, 1944). Also, Thierry's drawings of stems of some species of Chloranthus (e.g., C. japonicus Sieb.) do not suggest vessel presence. Stems of Chloranthus officinalis Blume are perennial and have been reliably reported to have vessels (Bailey and Tupper, 1918; Swamy, 1953). Possibly lack of vessels in stems of Sarcandra glabra is related to lack of secondary xylem accumulation. Bailey (1944) has demonstrated the tendency for vessels to be present first in secondary xylem of dicotyledons and then to progress phylogenetically into primary xylem. a trend documented bv the data of Bierhorst and Zamora (1965). ORIGINS OF VESSELS IN ANGIOSPERMS The traditional view that angiosperms were primitively vesselless, and that we see a primitive condition in extant vesselless woody dicotyledons, was offered by Thompson and Bailey (1916). although the reverse view, that of secondary acquisition of vessellessness by groups such as Winteraceae, was advocated by Jeffrey and Cole (1916). The idea of secondary vessellessness has been revived by Young (1981). I have offered objections to Young's arguments on the basis of morphology, ontogeny, and ecology (Carlquist, 1983). One may also object to his cladistic results, because certain of his presumptive vessel in which nearly intact porose membranes are visible. 10. End of a perforation plate in which a pit with intact membrane, above, is adjacent to three perforations with no remnants of pit membranes. Figure 6, bracket at upper left = 10 (im. Figure 7-10. magnification indicated by bracket, upper left in Fig. 7. which equals 5 jim.

1770 AMERICAN JOURNAL OF BOTANY [Vol. 74 groupings appear unlikely, e.g., Schisandraceae as the closest relative of Nymphaeaceae; Illiciaceae as a sister group of Tetracentraceae, Trochodendraceae, and Cercidiphyllaceae; and Ceratophyliaceae as the family closest to Chloranthaceae (which are not related to Piperales in Young's view). These and other novel alignments in Young's cladistics are not the central issue here, although they do affect the number of times one must hypothesize vessels to have originated if vessellessness is primary in angiosperms. The central core of Young's argument that vessellessness is secondary in angiosperms is based upon the number of times that vessels must be hypothesized to have originated in angiosperms. Although Young claims not to be influenced in all instances by parsimony considerations, the parsimony inherent in the number of times vessels must be hypothesized to have originated in angiosperms, if vessellessness is primary rather than secondary, is obviously important to Young. In a Takhtajanbased phylogeny that Young illustrates, Young claims that vessels must have originated 10 times in angiosperms to account for systematic distribution of vessels if vessellessness is primary. However, three of these events had to be hypothesized to account for vessellessness in Sarcandra, and now that vessels have been demonstrated for Sarcandra, only seven events are necessary conceivably fewer than seven if other phylogenetic schemes were used. Estimating the number of vessel-origin events required if one uses Young's own cladisticsbased phylogeny depends on whether or not one accepts his groupings, but is still about the same as for the Takhtajan tree, keeping in mind that Young's phylogeny does not include monocotyledons. Obviously, removal of Sarcandra from the list of vesselless woody dicotyledons requires us to hypothesize fewer events of vessel origin than we had to previously if we accept the idea of primary vessellessness. Let us suppose we must now hypothesize about seven events of vessel origin. Is seven too many? Several lines of evidence lead us to suppose not. Cheadle (1953) has made an excellent case for independent origin of vessels in monocotyledons and dicotyledons. Vessels in monocotyledons are in primary xylem, and originated phylogenetically in roots. In woody dicotyledons, vessels are absent in primary xylem of primitive groups (Bierhorst and Zamora, 1965), and arc believed to have originated simultaneously in secondary xylem of roots and stems simultaneously because of ontogenetic and systematic patterns of occurrence (Bailey, 1944). Nelumbo, although a dicotyledon, lacks secondary xylem and has a monocotyledonous growth form, so not surprisingly, vessels in that genus occur only in roots (Kosakai, Moseley, and Cheadle, 1970). Origin of vessels in Nelumbo is clearly independent of vessel origin in woody dicotyledons, as is that in monocotyledons. The organographic distribution of vessels in dicotyledons as compared to monocotyledons does offer the possibility that a group of dicotyledons with vessels in secondary xylem but none in primary xylem could have given rise to a taxon, such as Nymphaeaceae. that has only primary xylem and is vesselless. This possibility does not, however, counter the Thompson-Bailey idea that angiosperms were primitively vesselless. A most important line of inference about probable number of times vessels may have originated in angiosperms has not been cited in discussions. The well-known trends of specialization in vessels and other xylem features as delineated by Bailey and Tupper (1918), Frost (1930a. b, 1931), and Kribs(1935, 1937) have not been questioned by Young (1981). The major trends embodied in these papers are claimed to be essentially irreversible (Bailey, 1944; see Carlquist, 1980, for a discussion). These trends were established by means of statistical correlations, e.g., primitive rays are common in species with scalariform perforation plates, rare in species with simple perforation plates. So obvious that it has never been mentioned is the fact that given the large number of dicotyledons, representing a large number of families employed by the Bailey group in reaching these conclusions, the trends in vessel specialization could only have occurred in a highly polyphyletic manner. In other words, the transition from scalariform to simple perforation plates must have occurred many times in many phylads independently, and one can, in fact, cite systematic distributions that illustrate this probability. If vessel specialization has occurred in a highly polyphyletic fashion, vessel origin probably has also occurred polyphyletically. because the two phenomena are intercontinuous. If one hypothesizes dicotyledons to have been primitively vesselless, one must imagine, however, that the vesselless ancestral stock contained some degree of floral diversity. I do not find this difficult to envision, and the six or so events of vessel origin (four if we remove monocotyledons and Nelumbo) would have been in groups that depart but little from what most imagine to be the basic plan for the angiosperm flower. Interestingly, the highly mod-

December 1987] CARLQUIST WOOD OF SARCANDRA 1771 ified flowers of Sarcandra would represent a rather sharp departure from that basic plan, and with the removal of Sarcandra from the vesselless list, the four residual families (Amborellaceae, Tetracentraceae, Trochodendraceae, Winteraceae) become relatively coherent in terms of floral plan (e.g., all have several carpels separate to varying degrees, helical arrangement of some floral parts, no adnation, etc.). We can more easily imagine a relatively coherent vesselless group like this than we can imagine a highly diverse group of dicotyledons in which no vessel origin had occurred. One can then easily imagine that offshoots of a relatively coherent vesselless group developed vessels, and that this, in turn, permitted radiation in other aspects. There seems considerable evidence that primitive angiosperms were restricted to mesic habitats, and that vessel origin, followed by vessel specialization, may have permitted accelerated radiation into new habitats more than change in any other characters (Carlquist. 1975, 150 ff.). The ecological advantages of vessel specialization are so great that acquisition and specialization of vessels within a phylad could easily account for extinction of vesselless precursors, leaving the few relict groups of vesselless dicotyledons in the mesic pockets where we see them today. Stress should also be laid on the close approach to vessel-like structure by tracheids in some of the vesselless groups, such as Bubbia (Carlquist, 1983). This may explain why these vesselless groups have persisted. The difference between these tracheids and vessels is not a, great one, and is evidently not difficult to traverse. With the discovery of vessels in Sarcandra, the hypothesis of primary vessellessness in angiosperms seems enhanced. LITERATURE CITED BAILEY, I. W. 1944. The development of vessels in angiosperms and its significance in morphological research. Amer. J. Bot. 31: 421-428.. AND B. G. L. SWAMY. 1948. A mborella trichopoda Baill., a new morphological type of vesselless dicotyledon. J. Arnold 29: 245-254., AND W. W. TUPPER. 1918. Size variation in tracheary cells. I. A comparison between the secondary xylems of vascular cryptogams, gymnospcrms. and angiosperms. Proc. Amer. Acad. Arts 54: 149-204. BIERHORST, D. W.. AND P. M. ZAMORA. 1965. Primary xylem elements and element associations. Amer. J. Bot. 52: 656-710. CARLQUIST, S. 1975. Ecological strategics of xylem evolution. University of California Press, Berkeley.. 1980. Further concepts in ecological wood anatomy, with comments on recent work in wood anatomy and evolution. Aliso 9: 499-553.. 1983. Wood anatomy of Bubbia (Winteraceae), with comments on origin of vessels in dicotyledons. Amer. J. Bot. 70: 578-590. CHEADLE, V. I. 1943. The origin and trends of specialization of the vessel in the Monocotyledoneae. Amer. J. Bot. 30: 11-17.. 1953. Independent origin of vessels in the monocotyledons and dicotyledons. Phytomorphology 3: 23-44. EICHLER. A. W. 1864. Bemerkungen iiber die struktur des Holzes von Drimys und Trochodendron sowie iiber die systematische Stellung der lctzercn Gattung. Flora 47: 449-455. FAGERLIND. D.. AND A. DUNBAR. 1973. Some electron microscopical methods for solving wood anatomical problems. Bot. Notis. 126: 519-533. FROST, D. H. 1930a. Specialization in secondary xylem of dicotyledons. I. Origin of vessel. Bot. Gaz. 89: 67-94.. 1930b. Specialization in secondary xylem of dicotyledons. II. Evolution of end wall of vessel. Bot. Gaz. 90: 198-212.. 1931. Specialization in secondary xylem in dicotyledons. III. Specialization of lateral wall of vessel segment. Bot. Gaz. 91: 88-96. HARMS. H. 1897. Ueber die Stellung der Gattung Tetracentron und die Familie der Trochodendraceen. Ber. Deutsch Bot. Ges. 350-360. JEFFREY, E. C, AND R. D. COLE. 1916. Experimental investigations on the genus Drimys. Ann. Bot. 30: 359-368. KOSAKAI. H.. M. F. MOSELEY, JR.. AND V. I. CHEADLE. 1970. Morphological studies of Nymphaeaceae. V. Does S'elumbo have vessels? Amer. J. Bot. 57: 487-494. KRIBS. D. A. 1935. Salient lines of structural specialization in the wood rays of dicotyledons. Bot. Gaz. 96: 547-557.. 1937. Salient lines of specialization in the wood parenchvma of dicotyledons. Bull. Torrey Bot. Club 64: 177-186. MEYLAN, B. A..ANDB. G. BUTTERFIELD. 1978. The structure of New Zealand woods. DSIR Bull. 222. DSIR, Wellington. NZ. SWAMY. B. G. L. 1953. The morphology and relationships of the Chloranthaceae. J. Arnold Arb. 34: 375-408.. AND I. W. BAILEY. 1950. Sarcandra a vesselless genus of the Chloranthaceae. J. Arnold Arb. 31: 117 129. THIERRY, R. 1912. Contribution a l'etude anatomique des Chloranthacees. Thesis. Universite dc Paris. THOMPSON, W. P.. AND I. W. BAILEY. 1916. Are Tetracentron. Trochodendron, and Drimys specialized or primitive types? Mem. N.Y. Bot. Gard. 6: 27-32. TIEOHEM, P. VAN. 1900. Sur les dicotyledones des groupe des Homoxylees. J. de Bot. (Paris) 14: 259-297, 330-361. WHITE. R. A. 1961. Vessels in roots of Marsilea. Science 103: 1073-1074. YOUNG, D. A. 1981. Are the angiosperms primitively vesselless? Syst. Bot. 6: 313-330.