IAWA Bulletin n.s., Vol. 1 (3), 1980 87

WOOD ANATOMY OF THORNEA, INCLUDING SOME COMPARISONS WITH OTHER HYPERICACEAE

by

Arthur C. Gibson Department of Ecology and Evolutionary Biology, University of Arizona, Tucson, Arizona 85721, U. S. A.

Summary The wood anatomy of the new genus Thor­ num virginicum (Holm, 1903) lacked descrip­ nea (Hypericaceae) is described and compared tions of secondary tissues. Nevertheless, with that of other presumed relatives in the sections of hypericaceous stems are available in family. Woods of Thornea are very similar to wood collections, and the goal of this study those of Hypericum and Triadenum but quite was to describe the woods of Thornea and to dissimilar to those of Cratoxylum, with which make comparisons with its putative relatives. Thornea presumably shares common ancestry. Materials and Methods Introduction Wood specimens from mature plants of Breedlove and McClintock (1976) proposed Thornea calcicola (StandI. & Steyerm.) Breedl. the genus Thornea to include two evergreen & McClint. 7 cm and 4 cm in diameter were fruticose species from Chiapas, Mexico and collected in Chiapas and air dried by Dr. adjacent Guatemala that were originally de­ Dennis Breedlove (36973, 37070, OS). These scribed as species of Hypericum. Thornea has specimens were also those used in the generic nine fertile stamens grouped in three fasci­ description. In addition, Breedlove provided cles of three each, three persistent and free small stems of T. matudae (Lundell) Breedl. & styles, tricarpellate ovaries developing into McClint. liquid-preserved in formalin-acetic three nearly separate dehiscent capsules, and acid-alcohol (Breedlove 40408, OS). Wood pink and white petals with parallel stria­ samples of T. calcicola have been deposited in tions, features characteristic of Triadenum. the Madison Wood Collection (MADw). On the other hand, Triadenum are herbaceous Air-dried blocks were sectioned after re­ perennials of wet temperate habitats, quite hydrating, on a sliding microtome and stained unlike the habitus of Thornea. with safranin. Macerations were prepared by Based on the studies by Robson (1956, Jeffrey's macerating fluid and used to ob­ 1972), Wood and Adams (1976) and Breedlove tain 50 measurements of length for elements, and McClintock (1976) suggested that Triade­ whereas other features were obtained from num and Thornea, respectively, are closely sections. Young stems of T. matudae were em­ related to Cratoxylum of tribe Cratoxyleae, bedded in paraffin, sectioned at 15 J.Lm, and subfamily Hypericoideae, having an indepen­ stained with safranin and fast green. These dent origin from Hypericum, which is external­ microslides were examined but not used in the ly similar to Triadenum. Robson (1977) generic diagnosis for older woods. Nonethe­ elaborated on the close relationships of Triade­ less, woods of the two species are qualita­ num and Thornea to Cratoxylum and Eliaea tively very similar. and not to Hypericum, and he defined three Intergeneric comparisons with Hypericoi­ tribes, Hypericeae, Vismieae, and Cratoxyleae, deae were made using wood microslides borrow­ in subfamily Hypericoideae to recognize those ed from the Harvard Wood Collection (from differences in flower colour, staminal composi­ Vestal, 1937) and Rancho Santa Ana Botanic tion, and fruit and seed features. Garden, Claremont, California. Materials exam­ Vegetative anatomy of Hypericoideae is very ined include species of Harungana, Psorosper­ poorly known. Useful surveys on woods of mum, and Vismia of tribe Vismieae; Triadenum Hypericaceae (including Guttiferae and Hyperi­ virginicum and numerous species of Cratoxy­ caceae s.s.) are in Vestal (1937), Record and lum of Cratoxyleae; and over 100 species of Hess (1943), and Metcalfe and Chalk (1950), Hypericum, including the segregate genus and Baas (1970) has provided illustrated Ascyrum (Adams & Robson, 1961), especially descriptions of woods in Cratoxylum and the least derived and most woody sections of Eliaea. The only anatomical study on Triade- the genus (Robson, 1977). 88 IAWA Bulletin n.s., Vol. 1 (3), 1980

Fig. 1-4. Thornea calcicola. - I: Transverse section, showing diffuse porous wood with faint growth rings; x 50. - 2: Tangential section, in which uniseriate and multiseriate rays can be observed; x 50. - 3: Transverse section; tissue is composed of vessels, libriform fibres, and rays but not axial paren­ chyma; x 540. - 4: Tangential section, in which vessel-element length can be observed; x 540. -­ Fig. 5-6. Triadenum virginicum (Hw 5649). - 5: Transverse section at same magnification as Fig. 3, showing general similarities in these two woods. - 6: Tangential section as in Fig. 4; x 540.