Studies of Floral Morphology in the Ericales. V. Organography and Vascular Anatomy in Several United States Species of the Vacciniaceae

1. Organography and vascular anatomy of the following United States species of Gaylussacia and Vaccinium are described in whole or in part: G. baccata, G. dumosa, G. frondosa, G. ursina, V. alaskaensis, V. angustifolium, V. arboreum, V. australe, V. berberifolium, V. brittonii, V. caespitosum, V. canadense (myrtilloides?), V. constablaei, V. corymbosum, V. deliciosum, V. dentatum, V. erythrocarpum, V. hirsutum, V. lamarckii, V. macrocarpon, V. membranaceum, V. myrtilloides, V. ovalifolium, V. ovatum, V. oxycoccos, V. pahalae, V. pallidum, V. paludicola, V. parvifolium, V. reticulatum, V. scoparium, V. simulatum, V. stamineum, V. uliginosum, V. vacillans, and V. vitis-idaea var. minus. These species include one or more representatives of ten of the eleven sections of Vaccinium and of two of the three sections of Gaylussacia listed for the United States. 2. All members of the Vacciniaceae studied are pentacyclic (the outer whorl of stamens opposite the petals), epigynous, actinomorphic, and perfect. All sections except Hugeria, Oxycoccus, Vitis-Idaea, and usually Uliginosa are pentamerous; those named are tetramerous. Above the "ovary" wall, which is interpreted as composed of undiverged calyx, corolla, stamens, and ovary wall, the corolla is sympetalous in all except Oxycoccus, in which the petals are free, and Hugeria, Polycodium, and Vitis-Idaea in which the petals are free for half or one-third their length. Gaylussacia has ten carpels rather than the five (four) found in Vaccinium; those in Gaylussacia are alternate with the petals and sepals, not in the same planes as would be expected; those in Vaccinium are opposite the petals. In all species the stamens have introrse anthers which terminate upward in long awns (tubules) which become hollow and through which the pollen is shed. In addition to these awns, long spurs occur on the stamens of Batodendron, Euvaccinium, and Uliginosa, intermediate and variable ones in Macropelma, short or very short spurs in Hugeria, Polycodium, and Pyxothamnus, and no spurs in Cyanococcus, Oxycoccus, and Vitis-Idaea. Two of the species of Macropelma studied also show a sterile extension at the base of each anther half. Pollen is in tetrads. There is no endothecium. The corolla varies from strongly revolute in Oxycoccus and Hugeria, through open campanulate in Polycodium, cylindrical or slightly urceolate in many species, to highly urceolate in a few species, particularly of Euvaccinium. Placentation is axile, the one ovule per carpel in Gaylussacia borne at the top of the locule and turned outward, the several to many ovules per carpel in Vaccinium borne on enlarged placentae. There is a nectariferous disk of varying size on the surface of the ovary between the point of divergence of the floral whorls and the style. 3. The vascular tissue in the pedicel forms a complete cylinder. In the majority of species this broadens at the base of the flower breaking up into ten (eight) bundles. From the inner corners of five (four) or occasionally of all ten (eight) of these, small bundles turn inward, then upward, and supply the placentae and ovules, that is, constitute the ventral carpel bundles. Five (four) of the major traces, in alternating positions, soon divide tangentially to form ten (eight). The outer five (four) of these are the median sepal traces; the inner five (four) supply the sepalad stamens. The other five (four) major bundles first give rise inwardly to bundles supplying the dorsal regions of the carpels and then, at varying levels, divide tangentially, the outer bundles supplying the corolla, the inner the petalad stamens. The level of these various separations is the major point of difference between the species. Varying numbers of small bundles extend from the stamen traces toward or to the base of the nectariferous disk. 4. Gaylussacia, with ten carpels, differs in the origin of the dorsal carpel bundles. These either are small bundles left between the ten major ones or they diverge laterally from one or both sides of the "petal" bundles. In G. frondosa usually all, and in V. macrocarpon many, sepals receive three traces arising independently from the central cylinder, each leaving a separate gap. In G. frondosa and G. ursina the sepalad stamen traces are independent in origin; and in G. dumosa, a few species of Cyanococcus, Polycodium, and Uliginosa the undiverged "sepal" bundle is very short. 5. Guard cells, or their initials, were found in the inner epidermis of the carpels in the majority of species of Vaccinium studied but not in Gaylussacia. Stomata occurred regularly in the epidermis of the nectariferous disk of all species studied. In all cases, although the guard cells showed some differential thickening, the stomata appeared to be non-functional. 6. The present study serves to confirm the sections already established for the United States species of Vaccinium. 7. A number of speculations about possible phylogenetic trends are indulged in, but because the United States species of Vaccinium and Gaylussacia probably represent the ends of long phylogenetic lines the centers of distribution of which occur in the tropics, no conclusions can be drawn about phylogeny within the Vacciniaceae or between the Vacciniaceae and other groups of the Ericales.