Botanical Journal of the Linnean Society (2001), 13.7: 197—210. With 27 figures doi:10.1006/bojl.2001.0483, available online at httpV/www.idealibrary.com on IDE

Wood anatomy of the endemic woody Asteraceae of St Helena I: phyletic and ecological aspects

SHERWIN CARLQUIST FLS

Santa Barbara Botanic Garden, 1212 Mission Canyon Road, Santa Barbara, California 93105, USA

Received January 2001; accepted for publication June 2001

Quantitative and qualitative data are given for samples of mature wood of all eight species of woody Asteraceae, representing three tribes, of St Helena I. The quantitative features of all except one species are clearly mesomorphic, corresponding to their mesic central ridge habitats. Corn midendrum rugosum has more xeromorphic wood features and occurs in dry lowland sites. Commidendrum species are alike in their small vessel pits and abundant axial parenchyma. Melanodendrum agrees with Corn inidendrum in having fibre dimorphism and homogeneous type II rays. The short fibres in both genera are storied and transitional to axial parenchyma. Elongate crystals occur in ray cells of only two species of Corn midendrum, suggesting that they are closely related. Wood of Commidendrum and Melanodendrum is similar to that of the shrubby genus Felicia, thought closely related to Commidendrum on molecular bases. Corn midendrum and Melanodendrum have probably increased in woodiness on St Helena, but are derived from shrubby ancestors like today’s species of Felicia. Petrobiurn wood is paedomorphic and indistinguishable from that of Bidens, from which Petrobium is likely derived. The two senecionid species (Senecio leucadendron = Pladaroxylon leucadendron; and Senecio redivivus =Lachanodes arborea, formerly Lachanodes prenanthiflora) also show paedomorphic wood. Wood of the various St Helena Asteraceae is consonant with relationship to African or South American ancestors that reached St Helena via long distance dispersal. Derivation from genera of Pacific islands or Austromalesian regions is considered less likely. However, DNA evidence is needed to clarify origins, times of colonization on St Helena and divergence from closest relatives, and the nature of evolutionary patterns. © 2001 The Linnean Society of London ADDITIONAL KEY — WORDS: — Astereae Compositae dispersal — ecological — wood anatomy Heliantheae — insular

— woodiness paedomorphosis — phytogeography — Senecioneae.

INTRODUCTION evidence. Increasingly, molecular data offer invaluable evidence of taxonomic relationships, their degree and Eight species of woody Asteraceae, representing three even timing. A preliminary classification of the family tribes, are endemic to St Helena I. (Melliss, 1875; based on cladistic study of macromorphological fea Ashmole & Ashmole, 2000; Cronk, 2000). Seven of tures has been offered by Bremer (1987), and clado these are trees, but C. rugosum differs from its con grams based on analysis of DNA have been presented geners in being a shrub up to 1 m tall (Cronk, 2000). by Jansen, Michaels & Palmer (1991). These have The St Helena Asteraceae have attracted attention superseded earlier schemes. The St Helena Asteraceae because of their arboreal status, although woodiness do not belong to basal groups of the family. Bremer of various degrees is not really rare in species of the (1987) and Jansen et al. (1991) find mutisioids (espe family, especially those of subtropical and tropical cially the barnadesioids, often now segregated as the areas. However, the St Helena Asteraceae include trees outgroup to the remainder of the family) and other once prominent and common on the island, but now tribes of the subfamily Lactucoideae to represent mostly scarce; older their disappearance and subsequent elements within Asteraceae. conservation efforts are discussed by Ashmole & Ash- The fioras of the Macaronesian islands (offshore mole (2000) and Cronk (2000). islands of Africa in the north Atlantic) have been Wood anatomy can offer only limited phylogenetic thought by some to be relictual in nature (e.g. Cronk, 1987, 1992). However, the reverse hypothesis, that ‘woody herbs’ of the Macaronesian islands are E-mail: [email protected] secondarily woody and have evolved that and other

0024—4074/01/100197 +14 197 $35.00/0 © 2001 The Linnean Society of London 198 S. CARLQUIST features relatively recently on the islands, was arborea (Roxb.) B. Nord., Melanodendrum integri espoused by Carlquist (1965, 1974). Recent studies in folium (G. Forst.) Hook. f., Petrobium arboreum (J.R. which DNA analysis is presented cladistically, have & G. Forst.) R. Br., and Pladaroxylon leucadrndron supported the idea of secondary woodiness and autoch (G. Forst.) Hook. f. The generic names Lachanodes and thonous evolution in Macaronesia in relatively recent Pladaroxy ion are used here in accordance with Cronk times in such genera as Echium, Gonospermum and (2000), although these two monotypic genera may well Sonchus (Böhle, Hilger & Martin, 1996; Francisco- be abandoned in favour of Senecio when DNA studies Ortega et al., 1995, Francisco-Ortega et al. 1996; Fran of them have been made. Material of Corn midendrurn cisco-Ortega, Jansen & Santos-Guerra 1996; Fran rugosum (Dryand.) DC. was also provided by the Royal cisco-Ortega et al., 2001; Kim et al., 1996). The flora Botanic Gardens, Kew; material was harvested from of St Helena can be viewed against the background of their living collections of endangered St Helena species these studies, although DNA-based analysis on the by Tim Upson (s. n.). The material of Corn midendrum St Helena flora is needed. Paedomorphosis in wood rotundifolium (Roxb.) DC. was provided by the Samuel anatomy (Cariquist, 1962), despite earlier scepticism J. Record collection under the number Yw-29783 when (Mabberley, 1975) has proved a reliable indicator to that collection was housed at Yale University. All of discriminating between primary and secondary wood the above wood samples were taken from larger stems iness (see Carlquist, 1980, 1988, 2001). of mature plants, and thus are comparable with each The geographical relationships of the St Helena flora other and with mature wood of other species. Material are of critical importance, because the distance of this of Felicia amelloides Voss, obtained from a commercial island from the African coast makes long-distance source, was cultivated in my home garden. dispersal a mechanism that must be considered. The Dried wood samples were boiled in water and stored St Helena flora (Cronk, 2000) is relatively depauperate in 50% aqueous ethanol (material of Felicia amelloides and does not contain any conifers or primitive an was taken from a living plant and preserved in 50% giosperms, and thus appears typical of what is expected ethanol). Sections were prepared with a sliding micro- on a remote volcanic island (with favourable ecology). tome and stained with a safranin-fast green com The data from wood anatomy does bear on geographical bination. Some sections were left unstained, air-dried relationships, and some comments can be offered even between clean slides, attached to aluminum stubs, and though the best evidence will be provided by DNA examined with scanning electron microscopy (SEM). analysis. Cronk (1992: 95) gives geographical affinities Wood portions of each species were macerated with for the woody genera of St Helena Asteraceae (re Jeffrey’s Fluid and stained with safranin. produced by Ashmole & Ashmole, 2000). None of these Vessel diameter was measured as mean vessel lumen claimed affinities include Africa, although Noyes & diameter. Figures for vessel grouping are means based Rieseberg (1999) find that the African genera Felicia on the convention: a solitary vessel = 1, a pair of vessels and Amelius branch from the base of the Astereae they in contact =2, etc. Vessel grouping varies within sec analyse, just before Corn midendrum. tions, and in some illustrations the degree of vessel Even if studies of wood anatomy cannot yield the grouping is not representative (Figs 1, 5). Terminology broader results of the phylogenetic relationships that follows that of the IAWA Committee on Nomenclature DNA studies can offer, wood anatomy remains a sens (1964). Fibre dimorphism occurs in six of the species, itive indication of specific and generic similarities and and in some, subdivision of the shorter fibres into differences. More significantly, wood anatomy tells strands illustrates a transition into formation of axial much about the ecology of a species (Carlquist, 1975), parenchyma. Note should be taken that the term ‘sub and thus is worth investigation on this basis alone. divided fibre’ here indicates a fibriform strand of cells, The St Helena climate is diverse, being dry on scrubby each of which is surrounded by a secondary wall, and slopes near the shoreline and quite moist in dense fern does not in any way refer to septate fibres. Septate forest along the summit ridge (Ashmole & Ashmole, fibres were not observed in any species of the present 2000; Cronk, 2000), Vessel features of the wood ana study. Libriform fibres are not subdivided into strands tomy Helena of the St Asteraceae provide quantitative unless that condition is specifically stated. For sim reflections of this diversity in ecology. plicity, paratracheal axial distributions are described separately from the distributions of shorter fibres, even MATERIAL AND METHODS if the shorter fibres are quite parenchyma-like. The difficulty of distinction (i.e. lack of wider difference Wood samples for six of the species of species of St between two length classes of libriform fibres) dem Helena Asteraceae were provided by the Royal Botanic onstrates clearly that fibre dimorphism is a path Gardens, Kew, from collections made by J. C. Melliss for origin of axial parenchyma, as claimed earlier (c. 1875, s.n.). These include Corn midendrum robusturn (Carlquist, 1958, 1961). Further comments on this (Roxb.) DC., C. spurium (G. Forst.) DC., Lachanodes phenomenon are offered by Baas & Zweypfenning ______

WOOD OF ST HELENA ASTERACEAE 199

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3 4 Figures 1—4. Wood sections of Commidendrum robustum. Fig. 1. Transverse section (TS); tangential bands of wider fibres above centre. Fig. 2. Tangential longitudinal section (TLS); most rays are multiseriate. Fig. 3. SEM photograph vessel of wall, showing elongate pit apertures and grooves connecting pit apertures. Fig. 4. SEM photograph of ray cells from TLS; numerous elongate prismatic crystals are present in ray cells. Figs 1, 2, scale bar (in Fig. 1) = 100 Jtm; Figs 3, 4, scale bar = 10 tim. 200 S. CARLQUIST

(1979) and by Welle & Koek-Noorman (1981). Mean 239 jim. Mean width of multiseriate rays at widest libriform fibre length was measured from macerations, point, 3.7 cells. Mean height of uniseriate rays, 42 jim. and includes both shorter and longer fibres in species Mean ray cell wall thickness, 1.0 jim. Most ray cell pits with fibre dimorphism. non-bordered. Shorter fibres and axial parenchyma storied, although not clearly so in all places (Fig. 6). Crystals absent in rays. No deposits observed in ray RESULTS cells or axial parenchyma. COMMIDENDRUM ROB USTUM (Figs 1—4) COMMIDENDRUM RUGOSUM Growth rings not clearly demarcated, probably present (Figs 9—11) in the form of shorter, wider fibres (Fig. 1). Vessels Growth rings not evident (but growth ring absence mostly solitary (Fig. 1). Mean number of vessels per probable because of cultivated provenance of speci group, 1.96. Mean number of vessels per mm2, 32. men). Vessels mostly grouped (Fig. 9). Mean number Mean vessel element length, 213 jim. Perforation of vessels per group, 2.04. Mean vessel lumen diameter, plates simple. Lateral wall pitting of vessels alternate 24 jim. Mean number of vessels per mm2, 101. Mean to transitional. Pit apertures of vessels often elongate vessel element length, 166 jim. Perforation plates and coalescent into grooves (Fig. 3). Mean axial pit simple. Lateral wall pits of vessels alternate, circular cavity diameter, 2.3 jim. Mean vessel wall thickness, to slightly oval. Inconspicuous grooves interconnect 3.0 jim. Libriform fibres dimorphic, the shorter wider some pit apertures. Axial pit cavity diameter, 2.3 jim. fibres mostly distributed as tangential bands (Figs 1, Mean vessel wall thickness, 2.8 pm. Libriform fibres 2). Mean libriform fibre length, 602 jim. Mean wall dimorphic, the shorter, wider fibres few in number. thickness of libriform fibres, 2.5 jim. Axial parenchyma Axial parenchyma abundant to scanty vasicentric. Ax scanty to abundant vasicentric. Axial parenchyma in ial parenchyrna strands of one or two cells. Multiseriate strands of two cells. Multiseriate rays somewhat more and uniseriate rays about equally frequent (Fig. 10). abundant than uniseriate rays (Fig. 2). Ray cells pro Rays composed of procumbent cells almost exclusively, cumbent, except for a few square cells at tips of multi- square cells present only at tips of multiseriate rays. senate rays. Mean height of multiseriate rays, 258 jim. Mean height of multiseriate rays, 161 pm. Mean width Mean width of multiseriate rays at widest point, 3.1 of multiseriate rays at widest point, 3.0 cells. Mean cells. Mean height of uniseriate rays, 73 pm. Mean height of uniseriate rays, 56 jim. Mean ray cell wall wall thickness of ray cells, 0.8 jim. Ray cell pits mostly thickness, 1.0 jim. Most ray cell pits non-bordered, simple. Shorter fibres and axial parenchyma in Shorter libriform fibres vaguely storied. Crystals pres distinctly storied (Fig. 2). Elongate crystals present ent in ray cells (Fig. 11). No deposits observed in axial in ray cells (Fig. 4). Dark-staining deposits in axial or ray parenchyma. parenchyma cells (Fig. 1) and ray cells (Fig. 2).

COMMIDENDR UM SPURIUM COMMIDENDR UM ROTUNDIFOLIUM (Figs 7 8, 13) (Figs 5, 6—12) Growth rings not clearly demarcated, possibly in Growth rings not readily evident, perhaps present in dicated by tangential bands of shorter fibres (Fig. 7). relation to some of the tangential bands of shorter Vessels mostly grouped (Fig. 7). Mean number of ves fibres (Fig. 5). Vessels soliary or grouped (Fig. 5). Mean sels per group, 2.36. Mean vessel lumen diameter, number of vessels per group, 1.68. Mean vessel lumen 46 pm. Mean number of vessels per mm2, 22. Mean diameter, 53 jim. Mean number of vessels per mm2, vessel element length, 184 jim. Perforation plates 35. Mean vessel element length, 224 jim. Perforation simple. Lateral wall pitting of vessels circular to oval, plates simple. Lateral wall pitting of vessels alternate alternate. Grooves interconnect pit apertures. Axial with some grooves interconnecting pit apertures. Mean diameter of vessel pits, 2.3 jim. Mean vessel wall thick axial diameter of pit cavities, 2.3 jim. Mean vessel wall ness, 3.0 pm. Libriform fibres dimorphic, the shorter, thickness, 3.2 pm. Libriform fibres dimorphic. Mean wider fibres distributed in tangential and radial bands length of libriform fibres, 552 jim. Mean wall thickness (Fig. 7). Mean libriform fibre length, 510 jim. Mean of libriform fibres, 2.4 jim. Axial parenchyma commonly libriform fibre wall thickness, 2.3 jim. Axial paren abundant vasicentric, less commonly scanty vasi chyma abundant vasicentric (Fig. 7). Axial par centric (Fig. 5). Axial parenchyma in strands of 1 or 2 enchyma in strands of two cells, but more commonly cells (Figs 6, 12). Multiseriate rays more common than undivided. Multiseriate rays more common than uni uniseriate rays (Fig. 6). Rays composed of procumbent senate rays (Fig. 8). Rays composed of procumbent cells almost exclusively; a few square cells at tips of cells except for tip cells of multiseriate rays, which multiseriate rays. Mean height of multiseriate rays, vary from square to rhomboid shapes (Fig. 13). Mean WOOD OF ST HELENA ASTERACEAE 201

1:.

8

Figures 5—8. Wood sections of Cominidendrum. Figs 5, 6. C. rotundifolium. Fig. 5. TS; vasicentric parenchyma around vessel groups is abundant. Fig. 6. TLS; wider parenchymalike fibres are adjacent to vessel at left. Figs 7, 8. C. spurium. Fig. 7. TS; short parenchymalike fibres form tangential and radial bands adjacent to vessels arid vessel groups. Fig. 8. Tangential section; multiseriate rays are short and composed of procumbent cells. Figs 5—8, magnification as in Fig. 1. 202 S. CARLQUIST

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Figures 9—13. Wood sections of Commidencirum. Figs 9—11. C. rugosum. Fig. 9. TS; vessels notably narrow. Fig. 10. TLS; most libriform fibres in this view are long, narrow and thick-walled, although a few wide short fibres (near right edge) are present. Fig. 11. SEM photograph of elongate prismatic crystals from TLS. Fig. 12. C. mtundifolium, radial section, showing band of axial parenchyma cells running vertically. Fig. 13. C. spurium, TLS showing predominantly procumbent shape of ray cells. Figs 9, 10, magnification as in Fig. 1; Fig. 11, scale bar=5 tm; Figs 12, 13, scale bar= 40 im. WOOD OF ST HELENA ASTERACEAE 203 height of multiseriate rays, 56 jim. Mean width of abundant throughout rays. Mean height of multi- multiseriate rays at widest point, 3.1 cells. Mean height senate rays, 1033 jim. Mean width of multiseriate rays of uniseriate rays, 56 jim. Mean wall thickness of ray at widest point, 3.7 cells. Mean wall thickness of ray cells, 1.0 jim. Some pits on tangential walls of ray cells cells, 1.3 jim. Some borders present on pits oftangential bordered. Shorter fibres and axial parenchyma storied, walls of ray cells. Axial parenchyma and shorter fibres sometimes irregularly (Fig. 8). Crystals absent in ray storied (Fig. 19); longer libriform fibres indistinctly cells. Deposits absent in ray and axial parenchyma. storied. Crystals absent in rays. Deposits absent in axial parenchyma, but some resin-like deposits ob MELANODENDR UM INTEGRIFOLIUM served in vessels. (Figs 14—17). Growth rings absent (Fig. 14). Vessels mostly grouped PLADAROXYLON LEUCADENDRON (Fig. 14). Mean number of vessels per group, 2.56. Mean (SENECIO LEUCADENDRON) vessel lumen diameter, 53 jim. Mean vessel element (Figs 22, 23) length, 300 jim. Perforation plates simple. Lateral wall Growth rings absent. Vessels solitary or in small clus pitting of vessels oval and alternate (Fig. 16), trans ters (Fig. 22). Mean number of vessels per group. 1.89. itional (Figs 16, 17) or pseudoscalariform (Fig. 17). Mean vessel lumen diameter, 63 jim. Mean number of Axial diameter of vessel wall pits, 5 jim. Grooves in vessels per mm2, 21. Mean vessel element length, terconnecting pit apertures present. Mean vessel wall 306 jim. Perforation plates simple. Lateral wall pits of thickness, 2.5 jim. Libriform fibres dimorphic, but the vessels circular to oval, alternate. Mean axial diameter shorter fibres are only slightly thinner-walled than the of pit cavities, 5 jim. Vessel wall thickness, 3.0 jim. longer libriform fibres. Mean libriform fibre length, Libriform fibres monomorphic, mean length 572 jim. 502 jim. Mean libriform fibre wall thickness, 2.0 jim. Mean libriform fibre wall thickness, 4.6 jim. Axial Axial parenchyma scanty vasicentric (Fig. 14). Axial parenchyma scanty vasicentric (Fig. 22). Axial par parenchyma in strands of two cells. Multiseriate rays enchyma in strands of two to three cells. Multiseriate more numerous than uniseriate rays (Fig. 15). Ray rays predominant, uniseriate rays uncommon (Fig. 23). cells predominantly procumbent, a few square or up Procumbent, square and upright cells about equally right cells present at tips of multiseriate rays. Mean common throughout rays. Mean height of multiseriate height of multiseriate rays, 141 jim. Mean width of rays, 987 jim. Mean width of multiseriate rays at widest multiseriate rays at widest point, 2.6 cells. Mean height point, 4.8 cells. Mean height of uniseriate rays, 153 jim. of uniseriate rays, 74 jim. Shorter libriform fibres in Mean wall thickness of ray cells, 1.1 jim. Most ray cell distinctly storied (Fig. 15). Crystals absent in ray cells. pits simple. Libriform fibres indistinctly storied No deposits present in axial or ray parenchyma cells. (Fig. 23). Deposits seen in a few vessels (Fig. 22).

PETROBIUM ARBOREUM LACHANODES ARBOREA (SENECIO REDIVIVUS) (Figs 18—21) (Figs 24—2 7) Growth rings absent (Fig. 18). Vessels solitary or in Growth rings absent (Fig. 24). Vessels solitary or in short radial clusters (Fig. 18). Mean number of vessels radial clusters (Fig. 24). Mean number of vessels per per group, 1.48 jim. Mean vessel lumen diameter, group, 1.84. Mean vessel lumen diameter, 53 jim. Mean 67 jim. Mean number of vessels per mm2, 11. Mean number of vessels per mm2, 49. Mean vessel element vessel element length, 329 jim. Perforation plates length, 360 jim. Perforation plates simple, but a very predominantly simple, but a very small number of few aberrant plates with numerous very fine bars perforation plates with numerous slender bars present present. Lateral wall pitting of vessels alternate (Fig. (not illustrated). Lateral wall pitting of vessels circular 26). Lateral wall pitting of vessel circular to oval, and alternate or transitional, axial diameter of pit alternate (Fig, 26), transitional (Fig. 26) or pseudo cavities, 5 jim. Mean vessel wall thickness, 5.0 jim. scalariform (Fig. 27). Axial diameter of vessel pit cav Libriform fibres dimorphic, the shorter fibres thinner ities about 5 pm. Mean vessel wall thickness, 2.1 jim. walled and often subdivided into strands of two cells Libriform fibres monomorphic, mean length, 739 jim. and therefore definable as axial parenchyma (Fig. 19). Mean libriform fibre wall thickness, 3.5 jim. Multi- Mean length of libriform fibres, 764 jim. Mean wall senate rays predominant, only a few uniseriate rays thickness of longer libriform fibres, 5 jim; mean wall present (Fig. 25). Procumbent cells present in central thickness of shorter fibrefaxial parenchyma, 2.3 jim. portions of rays, but square and upright cells common Axial parenchyma scanty vasicentric, intercontinuous throughout multiseriate rays. Mean height of multi- with bands representing fibre dimorphism (Figs 20, senate rays, 1143 jim. Mean width of multiseriate rays 21). Multiseriate rays present exclusively (Fig. 19). at widest point, 6.3 cells. Mean height of uniseriate Upright, square, and procumbent cells about equally rays, 106 jim. Mean wall thickness of ray cells, 1.2 jim. 204 S. CARLQUIST ;

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Figures 14—17. Wood sections of Melanoclenctmn integrifolium. Fig. 14. TS; vessel density is low. Fig. 15. TLS; most libriform fibres are wide, short; some fibres are indistinctly storied. Figs 16, 17. Vessel wall portions from radial sections. Fig. 16. Alternate and transitional pitting; axial parenchyma on either side of vessel. Fig. 17. Alternate, transitional, and pseudoscalariform pitting on vessel wall. Figs 14, 15, magnification as in Fig. 1. Figs 16, 17, scale bar in Fig. 16 = 20 gui. WOOD OF ST HELENA ASTERACEAE 205

I

Figures 18—21. Wood sections of Petrobium arboreuin. Fig. 18. TS; vessels mostly in radial clusters. Fig. 19. TLS; axial parenchyma and parenchymalike fibres to left of centre. Figs 20, 21. TS showing distribution of wider, shorter libriform fibres. Fig. 20. Strand of wider fibres apotracheal, between vessels. Fig. 21. Wider fibres in a radial strip, to the right of the vessels. Figs 18, 19, magnification as in Fig. 1; Figs 20, 21, magnification as in Fig. 12.

16. Fig. in as magnification 27, 26, Figs 1; Fig.

in as

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22—25, Figs pseudoscalariform. most pitting but vessel) of edge (right alternate pitting Some 27.

Fig.

alternate. Pitting 26.

Fig. wide. notably rays multiseriate TS; 25. high. Fig. density narrow, vessels T5; 24. Fig.

rectivivus). (Senecio arborea Lachanodes 24—27. Figs multiseriate. rays TLS; 23. Fig. low. density vessels wide, TS; 22.

leucadendron).

Fig. (Senecio leucadendron Pladaroxylon 23, 22, Figs of Senecioneae. sections Wood 22—27. Figures

1I1 23

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S. CARLQUIST 206 WOOD OF ST HELENA ASTERACEAE 207

Ray cell pits mostly simple. Libriform fibres in St Helena genera appear to have had woody ancestry, distinctly storied (Fig. 25). No crystals observed in as indicated by lack of paedomorphic features (see wood cells. No deposits observed in axial or ray par Carlquist, 1962, 1988, 2001) in the wood. An increase enchyma. in stature from shrubs to trees during evolution of Commidendrurn and Melanodendrum on St Helena would SYSTEMATIC, GEOGRAPHICAL AND HABITAL be consistent with data available. If paedo CONCLUSIONS morphosis were present in these woods, one would hypothesize evolution from herbaceous or near-herb Corn midendrum and Melanodencirum are closely aceous to woody, rather than increase in plant size paired in the treatment of Hoffmann (1890). This within an already woody (i.e. shrubby) phylad. Cronk closeness is evidenced in wood anatomy by the presence (1992) had suggested relationship between the pair of fibre dimorphism (for a discussion of this concept in of St Helena genera and Austromalesian genera of Asteraceae, see Carlquist, 1958, 1961, 1988, 2001). Astereae such as Olearia. This relationship would The shorter, wider, thinner-walled fibres in the two seem unlikely on the basis of distance between the genera are wider and also, in general, more clearly Austromalesian localities of Olearia and St Helena, storied than the longer, narrower, thicker-walled because long-distance dispersal must be hypothesized fibres. The shorter fibres of Corn midendrum and Mel for St Helena. St Helena is a volcanic island, and no anodendrum are morphologically transitional to axial connection to any continental land mass has ever parenchyma. In all species of both genera, grooves been demonstrated (Ashmole & Ashmole, 2000). Long- interconnect pit apertures in vessel walls. Further, distance dispersal of the St Helena Asteraceae by Commidendrurn and MelanodencLrurn share Homo oceanic drift, as suggested by Ashmole & Ashmole geneous ‘ipe II rays (for definition, see Carlquist, (2000) is unlikely, because no Asteraceae have been 1988, 2001), whereas most Asteraceae have hetero demonstrated to have achenes viable after soaking in geneous or paedomorphic rays. Generic characters seawater. Olearia is not the most likely relative: its shared by the species of Commidendrum include rel wood differs from that of Cominidendron and Mel atively abundant (for the family) paratracheal axial anodendrum by lacking fibre dimorphism and by parenchyma and vessel wall pits with small cavity having heterogeneous rays (Cariquist, 1960). diameter (c. 2.3 pin). In Melanoctendrurn, in contrast, The family Asteraceae is probably basically woody paratracheal axial parenchyma is scanty, and vessel (Carlquist, 1966), a conclusion reached by cladistic pits are larger (c. 5 jim). The present treatment of studies using macromorphology (Bremer, 1987) and the two genera is justified, therefore. Corn midendrum molecular data (Jansen et al., 1991). However, rugosum shares with C. mbusturn the unusual feature some phylads of Asteraceae have probably changed from of elongate crystals in ray cells, and is probably an moderately woody to herbaceous, judging indicator of close relationship between the two species. from clado grams available (Bremer, 1987; Jansen The quantitative vessel features of C. rugosum differ et al., 1991). Some herbaceous from those of the other species and relate to differences phylads of Asteraceae have de in ecology, discussed below. veloped secondary woodiness, a phyletic trend in dicated Sections of moderately small stems of Felicia amel by cladograms such as those of Bohle et al., bides reveal the same qualitative features seen in 1996; Francisco-Ortega et al., 2001; Kim et al., 1996 Corn midendrum and Melanodendrum, although the and others cited in the Introduction. Paedomorphosis wood of F amelboides is somewhat more juvenile in wood has proved to be a viable indicator of secondary because of sample size. A close relationship between woodiness (Carlquist, 1980, 1988, 2001). Although Febicia and the two St Helena genera of Astereae is paedomorphosis in wood is not indicated in the Corn justified on the basis of wood anatomy. Wood of Felicia midendruni—Melanodendrum line, it does occur in the was studied because Noyes & Rieseberg (1999), in a species discussed below. DNA-based cladogram of Astereae, place Felicia and Although a few anatomical data on Petrobium were Amelbus as basal (but adjacent) to Corn midendrum. presented earlier (Carlquist, 1957), no wood data The affinities of Comrnidendrurn and Melanodendrum were presented then or in the survey of Heliantheae seem clearly to lie with the African genera of Astereae (Cariquist, 1958). The wood description given above is Febicia and Amellus, although DNA data from a larger the first to be offered. The wood of Petrobiurn exhibits number of genera of Astereae would, of course, be a number of distinctive features. One of these is fibre desirable. Hoffmann (1890) recognized 50 species of dimorphism: the longer fibres are vaguely storied, the Felicia, all shrubs, mostly from southern Africa. The shorter fibres more clearly storied. The short fibres, woody (albeit non-arborescent) nature of Felicia, and although not subdivided, are distributed in bands and the opposite leaves of Febicia and Amelbus are shared strands and could be considered transitional to axial with Cornrnidendrum and Melanodendruin. The two parenchyma. A survey of my wood sections of Bidens,

woodiness

increased to leads that factor selective the is for evidence offer not does but Senecioneae, Helena St

inbreeding of

avoidance that concept their sequently, the for areas source as Australasia and America South

con

and

problem, a not

is inbreeding where those claims (1992) Cronk senecionids. Helena St both for

as

such

areas

continental on woodiness secondary relative close a possible as New Zealand of howea Lord

of mention omit

(1996) al. et Böhle Andes. the in mentioned (1987) Cronk tribe. the within primitive

forest cloud

of areas in or Europe southern California, is Senecioneae Helena St the of habit caulous”

southern of those as such frost, with minimal climates “pachy the that (1874) believed Mabberley specified.

Mediterranean-type of areas of species in evident is not was but it relative, as the hinted was Islands

woodiness increased species, herbaceous of number Fernandez Juan the on Robinsonia Perhaps cified.

an alongside considered are other not appreciable families spe the are islands although Islands”, American

and Lamiaceae Asteraceae, If on islands. forms growth South the of Senecionieae ‘woody to similarities show

woodier of evolution in significance be greater of may species St Helena two the that claimed further (1975)

other factors 1974), (Carlquist, on islands evolution Mabberley assertion. his for reasons the detailing

to plant important factor a is obviously inbreeding without Africa”, in nothing resemble ‘they that claimed

that avoid features for selection Although 1996). al., et but Senecio, within species two the placed (1975)

1996; al., Kim et Bohle 1996; Rahn, 2001; 1996, 1995, Mabberley Africa. E. and Cameroons, Po, Fernando

al., et 1995; Francisco-Ortega Funk, & (Wagner cepted from species with along Senecio, of Arborei section

ac widely is now on islands woodiness Secondary the within species two the treated (1890) Hoffmann

Asteraceae. Pladaroxylon. and Lachanodes genera, monotypic two

St the Helena in change evolutionary and colonization into been placed have Senecioneae Helena St The

of timing relationships, clarifying set in data other bium.

any than more powerful prove data will Molecular for Petro woodiness secondary probable indicate and

Asteraceae. Helena St the data on clock’ ‘molecular 1962), (Carlquist, of dicotyledons wood in morphosis

We need other Asteraceae. or by those St Helena of paedo of to criteria correspond Petrobium of histology

occupancy an unbroken for evidence no is there over, ray and bars, fine with plate perforation occasional

I. More St Helena occupy currently that Asteraceae elements, vessel long The tissue. ray the of half least

of phylads to belong grains these that assurance no at comprise cells upright the Rather, plants. woody

is

there correct, are to Asteraceae referred grains in truly typical as is rays of the layer cell marginal a

pollen St the Helena of dating the and identification and tips to restricted not are and of Petrobium, rays

the that Assuming cladograms. those to according multiseriate in occur cells Upright 1966). (Carlquist,

later,

appreciably appeared Senecioneae and theae jim 282 habitats, mesic from Asteraceae of elements

Helian Astereae, 1991).

al., et Jansen 1987;

(Bremer, vessel for figure mean the than higher is (329 jim)

America South in barnadesioids with begun have must Petrobium of length element vessel mean The

the family that

now shows Evidence 1968). Baker, alliance. this within pathways precise soon identify will

&

I.

(Muir St Helena on BP Myr 9 deposit Pliocene data molecular Hopefully, conclusion. this from depart

an

early in of Asteraceae of pollen report a is There to reason see no I agree.” we which with hypothesis

suspected. be should a ancestor, Bidens-like a from derived dependently

woodiness ion, secondary and Piadaroxy in Lachanodes presumably were and Fitchia Oparanthus both to

genera the under recognized species the in and 2001), rise gave which lineage the Polynesian and Petrobium

1988, 1962, date (Carlquist, to studied instances the Atlantic south the that stated 450) has 417, (1974:

in

patterns these for account ancestors Herbaceous ‘Carlquist quote the offer (1997) Wagner & Shannon

paedomorphosis. xylary of indicative are Petrobium, of this. to doubt one lead would alone Oparanthus

those

like Senecioneae, I. Helena the St of histology of localities Polynesian the and St Helena between

and

ray lengths element vessel great relatively The distance the but Petmbium, and Oparanthus between

contrary. the to a relationship hypothesized (1992) Cronk lationship.

evidence persuasive is there unless expected be should re close of indicator an not is feature single this

St

to Helena close area source a that so islands, oceanic but corollas, disk quadrimerous share Petrobium and

of

other with those are congruent 1875) (Melliss, fauna Oparanthus birds. migratory via probably dispersal,

and

flora St Helena the and Australasia, or Islands long-distance by America South or Africa from either

Fernandez Juan the than closer is South America St Helena reached has that Bidens of a derivative also

continental or Africa Certainly Senecioneae. I. Helena likely very is Petrobium colonizations. later several)

St

the for area a as source Africa to exclude reason no (probably more or one represent Bidens of species

see

I studies, such of outcome the Pending analysis. insular Pacific whereas islands, Pacific colonized has

DNA of by

means species St Helena the of affinities of that Bidens derivatives likely are Oparanthus and

the

of determination accurate delay will Senecio genus Fitchia genera. in seen these also not features no sesses

the

size of large the Unfortunately, interpretation. this pos Petrobium that reveals Oparanthus and Fitchia

S. CARLQUIST 208 WOOD OF ST HELENA ASTERACEAE 209

on Macaronesian islands is dubious. These authors REFERENCES even go so far as to declare growth forms of some of the Canarian Echium species as anon-adaptive”, Ashmole P, Ashmole M. 2000. St. Helena and Ascension without giving any evidence for this designation. Island: a natural history. Oswestry, England: Anthony Nelson. Baas P, Zweypfenning RCVJ. 1979. Wood anatomy of the Lythraceae. Acta Botanica Neerlandica 28: 117-455. ECOLOGICAL CONCLUSIONS Böhle U-R, Huger HH, Martin WF. 1996. Island col onization and evolution of the insular woody habit in All of the the woody St Helena Asteraceae except for Echium L. (Boraginaceae). Proceedings of the National Corn midendrum rugosum occur in wet forest (Ashmole Academy of Sciences, USA 93: 11740—11745. & Ashmole, 2000; Cronk, 2000). Commidendrum ru Bremer K. 1987. Tribal interrelationships of the Asteraceae. gosum occurs in lowlands, especially in steep valleys Cladistics 3: 210—253. above the coast, and may have commonly occurred on Cariquist S. 1957. The genus Fitchia (Compositae). Uni lowland flats in earlier times (Cronk, 2000). Vessel versity of California Publications in Botany 29: 1—144. Carlquist features of woods tend to be a sensitive indicator of S. 1958. Wood anatomy of Heliantheae (Corn positae). Tropical Woods 108: ecology, as shown for the southern California flora by 1—30. Cariquist S. 1960. Wood anatomy of Carlquist & Hoekman (1985). The mesomorphy ratio Astereae (Compositae). Tropical Woods 113: 54—84. (vessel diameter times vessel element length divided Cariquist S. 1961. Comparative plant by number of vessels per mm2 of transection) anatomy. New York: is the Holt, Rinehart & Winston. figure that proved most useful in that study. Cariquist Carlquist S. 1962. A theory of paedomorphosis in dico & Hoekman (1985) report figures for this ratio for tyledonous woods. Phytomorphology 12: 30—45. woods of desert shrubs (21), chaparral (67), and sage Cariquist S. 1965. Island life. Garden City, New York: scrub areas (81) of southern California. Mesomorphy Natural History Press. ratios are also given for woody plants of riparian area Cariquist S. 1966. Wood anatomy of Compositae: a summary, (106) and for mesic woodland areas (1950). The lowest with comments on factors controlling wood evolution. Aliso mesomorphy ratio value among the woods of St Helena 6: 25-44. I. Asteraceae is that of Commid.endrum rugosum (39), Cariquist 5. 1974. Island biology. New York: Columbia which is in line with the values cited for shrubs from University Press. dry areas of southern California. Mesomorphy ratio Carlquist S. 1975. 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Ecological wood anatomy of the woody southern California flora. wider vessels that permit greater transpiration. Be IAWA Bulletin, n.s. 6: 319—347. cause there are no weather stations in the various Cronk QCB. 1987. The history of endemic flora of St. localities where the St Helena species of Asteraceae Helena: a relictual series. New Phytologist 105: 509—520. occur, it is impossible to determine whether there are Cronk QCB. 1992. Relict floras of Atlantic islands: patterns correlations between the mesomorphy ratio values of assessed. Biological Journal of the Linnean Society 46: 300 and above and soil moisture of the various summit 91—103. ridge localities of St Helena. Cronk QCB. 2000. The endemic flora ofSt. Helena. Oswestry, England: Anthony Nelson. Francisco-Ortega J, Barber JC, Santos-Guerra A, Febles-Hernandez R, Jansen RK. 2001. 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S. 210 CARLQUIST