Flora (1982) 172: 403 —491 Wood Anatomy of Buxaceae: Correlations with Ecology and Phylogeny SHERWIN CARLQuIsT Claremont Graduate School, Pomona College, and Raneho Santa Ana Botanic Garden Summary The family l3uxaceee consists of four genera, with the desert shrub Ssrnmonds’em dubiously mcludcd in the family as a fifth genus. Styloceras (Andean rain forest) has the most niesomorphic and primitive wood features, followed by &rrcococce and then by Buxus, which can be grouped closely with Notohuxus in terms of wood anatomy. Pachysormdra was excluded from this study because of its essentially herbaceous habit. For a small family, Buxaceae have a wide span in expression of wood features. Characters in Buxeceae s.c. which show a range within the family probably explainable in terms of ecology include vessel element length, number of vessels per muimc, vessel diameter, number of bars per perforation plate, presence or absence of helical thickenings in vessels and tracheids, and presence or absence of growth rings. The woods in the family can be ranked as highly mnesic (Stytoceras, Scmrcococca) to moderately mesic (Buxus, Notobuxus), with a few species in the latter pair of genera notably more mesomorphic in wood construction. Retention -of scalariform perforation plates throughout- Bmexoceee s.s. may be due to compensatory low transpiration capabilities of the foliage, which may have very thick cuticles and tend toward microphylly. Features which are susceptible to evolutionary interpreation but which do not bear as direct a relationship to ecology include ratio of tracheicl length to vessel element length, presence of tracheids with fully bordered pits, degree of aggregation of axial pamenchymna cells (diffuse, diffuse-in-aggregates, abaxial) and degree of cellular heterogeneity in ray histology. The ray types of Sercococce reflects a type of juvenilism, and scarcity of axial parenchyma in the genus also seems related to innovation of numerous shoots, each •with limited duration. Simrnondsia differs from Buxoceae s.s. in its desert habitat, its successive camnbia, and its anemophuily. i)istinctive features of wood anatomy (lack of acial parenchyma, juvenilisnu in ray histology, and presence of very short vessel elements with helical thickenings) can be attributed to the first two factors. No features of wood anatomy clearly rule out relationship to Buxeceae. Presence of tracheids in wood of $irnrnondsice may be related to the high selective value for tracheids in a desert environment; this feature (and the encyclocytic stomata) suggest affinity to Buxnceae, even if the genus is segregated in Sirnrnondsiaceae. Buxuceae have been claimed to be related to four major groups of dicotyleclons: Gelastro-les, E-uphorbioles, Hurncmnrelidaies, and 1-httosporeles. Of these, Euphorbiales shows the least degree of resemblance to Bnxaceee in terms of wood anatomy. The placement of the isolated Madagascan genus Diclyrneles may be related to the problem of placement of Buzoceae, and is discussed in this context. Introduction Wood anatomy of Buxaceae has been reported in condensed form by METCALFE & CHALK (1950). Their account and that of RECORD & GARRATT (1925) are generally 464 S. CARLQTT1ST accurate, and the present paper may be regarded as an amplification in several directions. Wood descriptions presently available are brief, or consist of a single species only, as in GREnuss’s (1959) account of B’uxus sempervrens. The present paper has been essayed as part of a survey of anatomy of families included by TH0RNE (1977) in Pittosporales. The genera of Buxaceae. as noted by METcALFE & CHALIC span a range in wood structure unusual for a single small family. This range is do cumented in quantitative form here (Table 1). The pattern of characteristics which emerges is compared to ecology of the species in the family. The family ranges from wet rain forest to moderately moist scrub, if one excepts the desert genus Simmondsia, often excluded from Buxaceae. Because the wood of Buxaceae ranges from strongly primitive to moderately specialized (highly specialized in Simmondsia), the comparison between evolutionary status of characters and their ecological distribution forms the basis for an inviting project. The relationships of Buxaceae have not been at all well understood. The traditional placement of B’uxaceae in Euphorhiales (or similar groupings) has yielded to a diversity of thought, with various authors opting for placement in such groups as Ha,ncrmeiidales (most recently TAKHTAJAN 1980), (‘elastrales (DAHLOREN 1977). or in a rosoid alliance such as Pittosporales (TH0RNE 1976). I)ata from wood anatomy are mostly inter pretable in terms of levels of wood evolution rather than indicators of affinity. There is growing appreciation of this among phylogenists. However, data from wood ana tomy can be expected to be usable to a limited extent in the construction of the natural system. The details of placement of the family are given in a later section of this paper. Buxaceae s.s. consists of five genera (distributions modified from Pa.x 1926-.-.-1928). Buxus frequently occurs on limestones and ranges from tropical meso-America into the West Indies, and from southern Europe and North Africa eastwards to Asia and offlying islands (Japan, Taiwan, Philippines. Borneo). Notobuxus is closely related to Buxus and consists of subsaharan African and Madagascan species which differ from .Buxus by having no pistillodes in male flowers, stamens without filments, and stamens four to eight as compared to four in Bu.xus s.s. (ADAMs0N. EsTERHUYsEN & PHILLIPS 1943). Sarcococca is a genus of understory shrubs, sprouting from near the base, native to southeast Asia (including Java. Sumatra. India, China, and Burma). A single species, S. conzattii (STANDLEY) JOHNsToN was recognized by JoHNsTON (1938, 1939). This species has baccate fruits. as in •S’a,cococca, but male flowers si.ir rounding a female flower as in Buxus (Sarcococca otherwise has bisexual flowers). More needs to be learned about this interesting situation. Pachysandra (southeast Asia and the eastern U.S.A.) is a genus of prostrate herbs, probably closely related to Sarcococca, which never develops much wood and has therefore been omitted from this study. The above genera are epresentative of temperate climates chiefly, and occur mostly in the northern hemisphere. They form a subfamily. Buxoideae. of Buxaceae. A second subfamily, Styloceratoideae, is formed by the genus Styloceras. native to warm tropical forests of Colombia, Ecuador, .Peru, and Bolivia. Simmondsia, variously Wood Anatomy of Buxaceae 465 included in Buxaceae or excluded as a genus incertae.sedis (TH0RNE 1976) is a shrub of southernmost California and adjacent Sonora and Baja California. It is listed at the end of Table 1 on account of its isolated features, and is discussed in a terminal section of this paper. Materials and Methods In other studies of wood anatomy, I have often been able to stuely wood anatomy from samples .1 collected in the field. in the present study, wood samples have been obtained from other cources, listed in Table 1 (herbarium abbreviations from H0LIemEEN & KNuKEN 1974; xylarium abbrevia tions from STERN 1978). The specimen of Sarcococca confusa (a species described from cultivation) was from material culti voted in the University Botanic Garden of Cambridge, England, and was collected for me through the kindness of P. F. YR0. The specimen of S. rvscifoliu, a species native to China, was collected from a cultivated shrub in Claremont, California. The wood of Simmoredsie was collected by James HanaicKsoN in Baja California, Mexico, a native habitat for this species whose specific- epithet is misleading. The remaining wood samples were obtained from wood collections, to whose curators I am grateful. The wood sample from the SJRw collection were PrOvided by MAI)w, where a set of Rrcoan’s wood collection is now housed. The locality data on these specimens is minimal. Provenances are as follows: Buxu$ beleurrcu, Balearic Islands; B. qio,nereta (MADw.205G9), Cuba; B. qlonrerete (USw-4300), Haiti; B. ha-rl-u.ndi-e, China; B. inicrophgliu var. netermed?e, Taiwan; B. microphyllee var. japoeeeca, Japan; B. sempc’rcirens, no collection data but probably European; B. wollichieene, India; Notob u.rus acuminate, \V . Africa; N. macowaaii, S. Africa (presumably the East London area); N. n-eetclensis, S. Africa (presumably the area from Pondoland to Durban, Natal); Styloceras laurifof turn, E. Ecuador. The Himalayan population termed Buxrrs wellichiana here is regarded by moSt authors as B. sempervirens. How ever, because of the distinctive nature of the wood, which doubtless reflects a more mesic habitat (1,800—3,000 in, Simla to Kumaon) than in typical B. semperviren.s, the segregate species name is used here for convenience. The comments on ecology of the various species. based on data gleaned from numerous finristic works, lint cannot be considered more than approximate because ireicroelirnatic conditions are all too often not specified when the habitat of a plant is given in floras. The best habitat data for the family is offered by RECoRD & GARO-url (1925), wood samples were boiled and then macerate(l and sectioned according to the usual techniques. Prior to sectioning, wood samples were soaked in ethylene diamine according to the general method outlined by KuKACUICA (1977), with variations in times dependent- upon the hardness of the wood. For aid in microtechnique, 1 un grateful to Mr. Vixca ECEHART. Anatomical Data The main basis for discussion is formed by the data in Table 1. Additional quali tative data are cited below, however, and comparisons between the results of the present study and those of earlier workers are offered. Because of the isolated nature of the genus uSimmondsia, all aspects of that genus are considered in a terminal section of the paper. Vessel Elements Vessel element length ranges from a mean of 440 tm in one collection of Noto bu.xws mac-owanii to a mean of 1,579 tm in one collection of S’tyioceras laurifolium.