BULLETIN OF THE TOBEEY BOTANICAL CLUB VOL. 97, No. 6, pp. 353-361 NOVEMBER-DECEMBER 1970 Wood anatomy of insular species of Plantago and the problem of raylessness Sherwin Carlquist1 Claremont Graduate Sehool and Baneho Santa Ana Botanic Garden, Claremont, California 91711 CARLQUIST, SHERWIN (Claremont Graduate School, Claremont, California 91711). Wood anatomy of insular species of Plantago and the problem of insular woodiness. Bull. Torrey Bot. Club 97: 353-361. 1970.—The most markedly woody species of Plantago are insular. Detailed anatomical descriptions, quantitative data, and photomicrographs are presented for woods of P. arborescens (Canary Islands, lowlands), P. maderensis (Ma­ deira, lowlands), P. webbii (Canary Islands, alpme areas), P. fernandeziana (Juan Fer­ nandez Islands, rain forests), and P. princeps (Hawaiian Islands, shady areas in rain forest). Vessel element length and width are greatest in the rain-forest species, least in the alpine species. These expressions seem clearly correlated with degrees of xeromorphy or mesomorphy. Plantago woods are all basically rayless, but rays are eventually formed in larger stems of the species from Macaronesia (the term given collectively to the Cape Verde Islands, Canary Islands, Madeira, Azores, and nearby islands). Rayless woods as exemplified bj' Plantago tend to occur in dicotyledons in which (1) eambial activity is limited or finite; (2) woodiness is phyletieallv in the process of increase, rarlier tha crease; (3) fusiform eambial initials are relatively short; and (4) juvenilism or paedo- morphosis occurs. The phenomenon of ^insular moodi­ duce during this period. In the Canaries. ness," the tendency" for insular representa­ P. arbort«c< ns can live through the mild tives of a taxonomic group to be more and more humid summers and thus last for woody than their continental counterparts, several years. In fact, in the relatively is well illustrated by Plantago. This world­ maritime climate of Santa Barbara, Cali­ wide genus is herbaceous, yet on various fornia, cultivated plants of P. arbor•<m islands of the world, woody species are pres­ also do this. ent. These have evolved, at least in part, Plantago arborescens is one of a series from several groups of herbaceous main­ of closely related Maearonesian species. It land plantagos. The Pacific insular species, occurs near sea level to about 400 m in the certain!}-, have been derived independently Canary Islands, and can be found with of those from the Maearonesian (Atlantic shrubby species of EcJiium and Sonchus islands. To be sure, no Plantago is markedly and other elements of the coastal scrub, woody, but the insular species do have more such as Hypericum, Aeonium, and legumi­ secondary xylem accumulation than their nous shrubs. Plantago arborescens does not closest mainland counterparts. grow in the wet laurel forest or in the I'hi at ago has arrived on many islands, pifiar. Contrary to its name, it is not really presumably by means of its characteristic tree-like: a large specimen rarely is more dispersal mechanism. Seeds are small and, than half a meter in height. The stem, at when mature and moistened by rain or the base, rarely exceeds 1-2 cm in diameter. otherwise, develop a gelatinous film that Plantago webbii is an alpine counterpart to fastens them to feathers or other animal P. arborescens, almost an alpine ecotype. parts. Plantago also seems to establish well It grows in the high, dry caldera of El on islands because of its weedy tendencies. Teide (ca. 3,000 m), Tenerife, Canary- I was surprised to find that in my garden Islands. Here it may be found with shrubby in Claremont, a Canary Island endemic, P. crucifers, Spartocytisus, and other alpine arborescens, became naturalized despite the plants. For ecological data and illustrations fact that the climate of Claremont is more of the Canary Island plantagos, the reader continental than that of the Canary Islands. may consult Burchard (1929), Lems (1960) These escaped plants are facultative an­ and Schenck (1907). nuals in Claremont: they germinate after autumn rains, grow into shrubs during win­ 1 Field and laboratory studies have been aided ter and spring, but then die during the by two grants from the National Science Founda­ summer. They are, however, able to repro­ tion, GB-4977X and GB-14092. Received for publication July 3, 1970. 3o-) 354 BULLETIN OF THE TORREY BOTANICAL CLUB [VOL. 97 Plant ago maderensis of Madeira occurs of this species, which may now be extinct, Dear sea level on Madeira, with Euphorbia. was available to me. Aeonium, Lytantkus, and shrubby cruei- The significance of Plantago woods lies fers. It is closely related to P. arborescens in their response by means of increased both in morphology and ecology, and may woodiness to the uniformity of insular cli­ I"' regarded as a vicarious species of the P. mates. These plantagos are, in fact, sensi­ arborescens group. tively adjusted to the ecological conditions riant ago princeps is a distinctive Ha­ in which they grow. They are not, in my waiian endemic. Unlike other Hawaiian opinion, relicts: they are all on volcanic plantagos, it has slender upright stems with islands of modest age. Apparently phyletic relatively long internodes. In habit it re­ increase in vessel-element length to suit calls some species of Dracaena. Xow ex­ mesic conditions can take place; if so, the tremely rare, Plantago princeps once was mechanism is a pertinent subject for in­ abundant in ravines, on cliffs, and near vest igation. waterfalls in the Hawaiian Islands. The Plantago woods are all rayless, at least stems, although upright, lack mechanical earlier in the ontogeny of a plant. The sig­ strength and the plants tend to lean on sur­ nificance of rayless woods in relation to rounding shrubs, or to grow up through habit, ecology, level of phyletic specializa­ such other plants. The wood sample used tion, direction of phylesis, and nature of in the present study was collected by Mr. wood ontogeny, needs to be understood. Melvern Tessene in the Aina IIo Valley, Data of the present paper are pertinent to Koolau Gap, Maui. This plant would fall this problem. into P. princeps var. la&ifolia according to Wood of Plantago princeps was cited the treatment of Rock (1920). Rock recog­ by the writer (1962) in such a context. A nizes numerous varieties of P. princeps. description of wood of Plantago, based on These might be termed subspecies accord- P. fernandeziana, was offered bv Metcalfe in-.'' to current concepts. I prefer, however. and Chalk (1950). to think of P. princeps as a single polymor­ Materials and methods. Woods of the phic species. In fact, P. princeps is appar­ Maearonesian species of Plantago were col­ ently fully interfertile with Hawaiian lected by the writer in the field. The largest plantagos of an entirely different appear­ plants available were taken for study. Some ance, including bog species such as P. samples were unsuitable for study, how­ pachyphyUa, P. hillebrandii. etc. (Melvern ever, because of markedly distorted wood Tessene. persona] communication). Ecologi- grain—stunted, twisted stems are common eal data and photographs of P. princeps in the Maearonesian species. The writer is and other Hawaiian plantagos are offered indebted to Mr. Melvern Tessene for the by Kock (1920) and Carl.piist (1970a). sample of P. princeps. The samples of P. Plantago fernandeeiana is a species of fernandeziana were provided through the rain forest in the Juan Fernandez Islands. assistance of Dr. Otto Solbrig, Dr. Fred Ms ecological situation is much like that of Meyer, and Dr. Richard H. Eyde. P. princeps. The internodes are shorter Wood sections and macerations were than in P. princeps. but it also tends to prepared according to the usual techniques. form unbranched upright stems topped by The wood samples available were reasonable leaf rosettes. Good photographs of P. fer- in size for a wood study, and samples with tinndi :inIKI and ecological information are too limited a development of secondary ided by Skottsberg (19S2). One can­ x vie in were deliberately omitted. For ex­ not be positive that P. fernamleziana is not ample, liquid-preserved stems of P. pachy- closely related to P. princeps, but it could jdndla could have been sectioned by means AVCII be an insular derivative from main­ of paraffin techniques, but the limited de­ land plantagos independent of other insular velopment of secondary xylem in this spe- Pacific species of Planiago, In the Atlantic. eies would, in my opinion, not have added the distinctive P. rob'uata, an endemic of significant information, at least with re­ St. Helena, is almost certainly not closely spect to the central concerns of the present related to the Maearonesian plantagos. For study. information and illustrations of P. robusta. Qualitative and quantitative data were the reader is referred to Melliss (1875) and obtained from six collections of the five Carlqnist (1965). Unfortunately, no wood species studied here. In rayless or near- L9T0 CARLQUIST: WOOD ANATOMY OF PLANTAGO 355 rayless woods, ray measurements are not jacent to vessels may perhaps be termed axial of significance. The diameter of libriform parenchyma cells by virtue of their pits, which ider apertures than typical for libriform fibers was obtained by measuring the widest fibers. A very few such cells subdivided into strands point of liber diameter as seen in a macera­ of S cells were observed. Growth rings absent, dif­ tion and averaging 50 such measurements. ferences from one portion of xyloin to another too A figure for vessels per group was not com­ minor to permit distinction as true growth rings. puted because groupings in /'. fmiiindezi- No storied structure observed. No resin-like de­ ana Fi& 3) are almost infinite; vessels posits present. in P. webbii are often as narrow as libri­ PLANTAGO MADEBENSIS Decne., Carlquist 2622 form fibei's and therefore difficult to iden­ (B8A), Ribeiro Brava, Madeira (Figs.