Taxonomic and Ecological Implications of Foliar Morphoanatomy in Cephalanthus (Naucleeae, Rubiaceae)

ROMERO MARIA F.;; SALAS R.M.; A. M. GONZALEZ

SYSTEMATIC BOTANY

AMER SOC PLANT TAXONOMISTS

Lugar: Laramie; Año: 2019 p. 378 - 397

0363-6445

Cephalanthus belongs to the tribe Naucleeae, and is characterized as a shrub to a small tree, mainly from the lowlands, with (2?)3-4-verticillate leaves. We hypothesized that the foliar morphoanatomy of Cephalanthus species provides informative characteristics to our taxonomic study and that their leaves present adaptations to waterlogged habitats. To test these hypotheses our aims were to describe the macro- and micromorphology and anatomy of leaves in all the Cephalanthus species. The species were studied using light and scanning electron microscopy based on fresh, fixed, and herbarium material. We describe and characterize leaf disposition, shape, size of blade and petiole, characteristics of the epidermis and indumenta, including the micromorphology of the cuticle and stomata, and the types of leaf domatia, if present. The anatomy of the petiole and leaf blade was also analyzed, including the mesophyll, vascular systems, ontogeny of the stomata, presence and typification of oxalate of calcium crystals (sand, druses, duplex idioblasts and spherites), and their distribution in the foliar tissues. Certain uniformity in the morpho-anatomical characters allows us to define the genus Cephalanthus, but inside this uniformity also we can also differentiate between the species by means of a dichotomous key. The presence of domatia in pockets in C. occidentalis in contrast to the tuft of hairs in C. salicifolius and C. tetrandrus shed light on the taxonomic delimitation of the former because historically they were considered a single species. Cephalanthus species show variability in the [micro] morphological characters but have a strong uniformity in anatomical organization. The leaves of Cephalanthus show adaptations to seasonally environments, some of them are typical hydromorphic traits (i.e. thin cuticle and cell walls, single layered epidermis, mesophyll with large intercellular spaces and few trichomes), while other reflect adaptations to their heliophilic habitat and tolerance to dry periods (i.e. heterobaric leaves).