ANATOMY Aid SYSTEMATIC POSITION of CENTAURODENDRON and YUNQUEA (COMPOSITAE)
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Reprinted from BRITTOXA, VoL 10, No. 2, April 1958 Printed in U. S. A. ANATOMY AiD SYSTEMATIC POSITION OF CENTAURODENDRON AND YUNQUEA (COMPOSITAE) SHERWIN CARLQUIsT Claremont Graduate Sehoo, Ilaneho Santa Ana Botanic Gardeit Claremont, California I I ANATOMY AiND SYSTEMATIC POSITION OF CENTAURODENDRON AND YUNQUEA (COMPOSITAE) SHERWIN CARLQUIST Claremont Graduate School, Raneho Santa Ana Botanic Garden Claremont, California The genera Centaurodtnciron and Yunquea are remarkable in that they are both “rosette trees” which have been interpreted as belonging to the tribe (yn areae (Skottsberg l93 and are endemic to the island Masatierra in the Juan Fer nandez Islands. (‘ nta,rodendro’o consists of two species. (‘. (11u(aen1Juh( S .JOIIOH and (. palin.iforme Skottsherg, whereas Ynnquea tenii Skottsberg is the single species of its genus. The main purpose of the present study is to show how anatomical evidence bears on the systematic relationships which have been pro posed on the basis of gross morphology, Because (entauroclendron and Ynnquea are the only arboreseent genera referred to Cynareae, and because they show little superficial similarity to other Cynareae in vegetative characters, a study of their anatomy is desirable in determining if this is, indeed, the correct dis position of these genera. A secondary problem is created by the genus Yunquee, which Skottsberg (1929) erected on the basis of scanty egetative material. Allhough subsequent collections have furnished no flowers of this plant, which evidently flowers with extreme infrequency, anatomical data from the vegetative portions of the plant and from recently collected mature achenes appear to be decisive in assessing Skottsberg ‘s (1 929) suggestion that it should be regarded as a genus closely related 10 (‘Entuu,’odI ndi’on. Individuals of iunquea. are rare, and the localities in which they grow are difficult of access (Kunkel 1957; Skottsberg 1953). It may become extinct, as has so much of the antoelithonous Juan Fernandez vege tation,withont hiaviiig been. collected in the flowering state. The recent discovery (Skoltsberg 1957) of (]entaurodendron palmfforme is significant, for this species shows greater similarity to Yunquea than does C. (lracaenonlnc. Moreover, anatomical characters can be used in contrasting the two species of (n to urodendron. MATERIALS ANt) METHODS Centaurodendi’on druea.enoides is only slightly more abundant than C. patmi forome or Yunqnui. but has been collected, at rare intervals, in flower. Therefore, the writer was able to use herbarium material for studies of the anatomy of inflorescence parts. Except for this material, listed below, the present study was based entirely on material collected by Dr. Skottsberg or collectors who assisted him during ins visit to the islands in 1955. Skottshcrg’s own collections were preserved in dilute ethyl alcohol, and consisted of stems, leaves, and shoot tips. wood samples were also collected and dried. Although no herbarium specimens were prepared to document these collections, which in a sense are doenniented by Dr. Skottsherg’s intensive knowledge of the Juan Fernandez flora. lhc writer is retaining the liqoid-preserved samples on which the studies were based. The specimens are as follows: BRITTONIA 10: 78-93, April 1958. —78- 1958] CARLQUIST: CENTAURODENDRON AND YUNQUEA 79 Centaurodendron dracaenoides. Vegetative. Coil. C. Skottsberg, Sept. 3, 1955. Portezuelo do Villagra, Masatierra. Liquid. Same. Flowering. Coil. H. Weber, without data, 1937 (University of California Herbarium, Berkeley. Centaurodendron palmiforme. Vegetative. Coil. C. Kunkel, Sept. 3, 1955. Masatierra. Dried. Same. Weathered infiorescence. Coil. B. Sparre, Jan. 10, 1955. Masatierra. Dried. Same. Old stem. Coil. B. Sparre, March 5, 1955. Masatierra. Dried. Yunquea tenzii. Vegetative. Coil. C. Skottsberg, June 3, 1955. El Yunque, Masatierra. Liquid. Same. Aehenes. Coil. G. Kunkel, June 3, 1955. El Yunque, Masatierra. Dried. The writer wishes to express sincerest appreciation to Dr Skottsberg for the material mentioned, and to Dr T. H. Goodspeed, through whose good offices arrangements for these collections were made. The cooperation of the University of California Herbarium in allowing use of the specimen listed above is grate fully acknowledged. Herbarium material was prepared by treatment with 2.5 per cent NaOH in a 600 C oven. When material was sufficiently cleared and expanded by this method, it was washed and stored in 50 per cent ethyl alcohol. Both the alcohol- fixed material and the “revived” herbarium specimen portions were dehydrated according to Johansen’s (1940) tertiary butyl alcohol series, and embedded and sectioned according to the usual techniques. Treatment with hydrofluoric acid for several weeks was found necessary for softening the rather sclerotic stems of Centaurodendron dracaenoides before dehydration. Sections were stained by means of tannie acid and ferric chloride, followed by a safranin-fast green combination. In addition to sectioned material, whole mounts of leaves, involue ral bracts, flowers, and pollen were prepared by the NaOH technique mentioned above, followed by dehydration and staining with safranin. The wood samples were sectioned on a sliding mierotome after boiling in water, followed by immersion for about six weeks in 36 per cent hydrofluoric acid. Stems of C. palmiforme were sectioned without such treatment. Safranin in absolute ethyl alcohol was employed as a stain. VEGETATIVE ANATOMY Leaves of Centaurodendron differ markedly from those of Yunquea in gross morphology. Yunquea has petiolate, toothed leaves with prominent ribs (corre sponding to the major veins) on the lower surface; the ribs and petiole have a light covering of uniseriate, non-glandular hairs. Centaurodendron leaves are sessile (rarely somewhat petiolate), nearly emarginate (the teeth obscure, although more obvious in C. palmiforrne), and smooth and glabrous on both surfaces. Study of foliar ontogeny demonstrates that leaves of the two genera are basically more alike than these differences would suggest, although study of their mature anatomy reveals additional characters which distinguish the genera. The shoot apex of Yunquea shown in Figure 1 serves to demonstrate the leaf origin in both of these genera. Leaf primordia originate in a spiral around the dome-shaped apical meristem. The meristem itself is rather clearly zonate. Three layers of tuniea are discernible, and the corpus contains a central mother- cell zone which has abundant pectic accumulations at cell interstices. Prominent rib-meristem action is initiated a short distance below the mother-cell zone. These clearly defined files of cells are not responsible for the formation of the entire pith, however, but only the central portion of it. The shoot apex of Centaurodendron dracaenoides shows the same features except that the groups BRTT’TONIA VOL. 10 of cells destined to become pith sciereids are deuiareated at an early stage, as mentioned below. Figure 2 shows the presence of two types of hairs on an immature petiole of Ynqttea. These trichomes may be classified as uniseriate non-glandular (top of photograph) and biseriate glandular (near top and bottom of photograph). Despite the glabrous nature of leaves in Ceo laurodendron, the uniseriate non glandular hairs are present on immature portions of herbage in that genus, just as they are in Yunqnea. On mature Yuiiquea leaves, uniseriate hairs are pre served only along the ribs on the lower surfaces of leaves, in the leaf axils, and on petioles. They appear to be wholly lacking on mature leaves of Ceniacrodc’n cI.roa. Degeneration of such uniseriate triehomes is evident in the stage shown in Figure 2. which is prior to the formation of pockets surrounding glandular hairs. The difference in vesture of leaves between Centavrodendron and lun qnea, then, is a matter of relative preservation of uniseriate hairs, which are present on young leaves in both genera. For the most part, the biseriate glandular hairs do not degenerate soon Rather, they become sunken into pockets (Figs. 4, 5) on both surfaces of the leaves, both in (‘c-n(aurodeadi’oa and fun queG. Glandular hairs on mature leaves, however, appear to be non-functional and collapsed. Although sunken biseriate glandular tricliomes have been demonstrated for i1ompos.itae only in a member of Mntisieae, Hesperornaunia (Carlqu:ist 1957a), they probably occur also in Cynareae, as Skottsherg’s reports (1929. 193s) of similar ‘‘glandular clots’’ in Centauiea suggest. The niature lamina of (cniaurodeudron cliacacnoith’s (Fig. 4) differs from that of Yunqnc (Fig. 5) in a number of respects. As mmotecl by Skottsherg (1938), two layers of palisade are characteristically present in C. droccceuoides, whereas a single layer occurs in fun quea. Moreover, the total number of ineso piiyll layers is greater in both species of Centeurodenthon. which have nine cell- layers, than in Yen qnea, which has six. Where veins occur, of course, layers are more numerous. Bundle sheaths are well developed in Centaurodcndron. and larger veins have conspicuous bundle-sheath extensions (Fig. 4, right). In addition, fibers are abundant around the larger veins (Fig. 4, right) and even some of the smaller veins (Fig. 4, left). In Yu’nquea, bundle sheaths are also present; veins with sheath extensions are those associated with a prominent rib on the lower surface of the leaf (Fig. 5, left). Fibers are present within the bundle sheaths of the larger veins, although they are less abundant and do not completely jacket a vein as they often do in Centanrodendron. The prominent teeth on the margins of Yuiiquea leaves are hydathodic in construction. The relatively obscure teeth of Centaurode’ndro’n leaves also have such a structure. Aside from the points mentioned above, structure of the lamina in the two genera is quite alike. Lamina structure of C. paliniforme was observed to be identical to that of C. dracaenomd.es in all respects. Petiole and Node. C’ntaurodendron lacks a clearly defined petiole. The narrowed portion of the leaf base subtending the lamina is shown for C. dracae’no’ides in Figure 3. This section corresponds to that illustrated diagram mnaticall in Figure 12.