Inflorescence and floral traits of the Colombian species of <em>Tristerix (Loranthaceae)</em> related to hummingbird pollination

Abstract

Abstract. Floral diversification in Loranthaceae reaches its highest peak in the Andes. The flowers of the exclusively Andean genus Tristerix exhibit tubular and vividly coloured flowers pollinated by hummingbirds. We studied inflorescence and flower morphoanatomy of the two Colombian species, T. longebracteatus and the highly endangered T. secundus. Both species have terminal racemes with up to 26 ebracteolate flowers, of which the proximal one opens and sets fruits first. The slightly irregular calyx initiation is followed by the simultaneous initiation of petals and the successive initiation of stamens. Anthesis is fenestrate, explosive, and triggered by the tension of the style against the abaxial petals, a mode so far not reported in Loranthaceae. Anthetic petals spread symmetrically in T. longebracteatus and asymmetrically in T. secundus. Nectar is produced by a supraovarial disk and by the petal mesophyll. Floral lifespan lasts up to 20 days. The hummingbirds Eriocnemis vestita and Pterophanes cyanopterus are the likely pollinators of T. secundus. Morphological traits are inconclusive to support one of the two competing sister group relationships that involve Tristerix, as the lack of cataphylls in renewal shoots links Ligaria and Tristerix, whereas the terminal inflorescences support its relationship with Desmaria and Tupeia.Resumen. La diversificación floral en Loranthaceae alcanza su máxima expresión en los Andes. Las flores del género Tristerix, restringido exclusivamente a dicha cordillera, exhiben flores tubulares y de color llamativo que son polinizadas por colibríes. Se ha realizado un estudio de la morfoanatomía de inflorescencias y flores en las dos especies colombianas del género, T. longebracteatus y T. secundus, esta última muy amenazada. Las dos especies tienen racimos terminales hasta con 26 flores ebracteoladas, de las cuales la proximal se abre y forma el fruto antes que las demás. La iniciación del cáliz, levemente irregular, es seguida por la iniciación simultánea de los pétalos y la iniciación sucesiva de los estambres. La antesis es fenestrada, explosiva y se activa por la tensión del estilo contra la comisura de los dos pétalos abaxiales, un modo de antesis hasta ahora no descubierta en Loranthaceae. Los pétalos en antesis se expanden simétricamente en T. longebracteatus y asimétricamente en T. secundus. El néctar se produce en un disco supraovárico y el mesófilo de los pétalos. El periodo entre la antesis y la iniciación del fruto dura hasta 20 días. Las especies de colibrí Eriocnemis vestita y Pterophanes cyanopterus son los visitantes y probables polinizadores de T. secundus. Los rasgos morfológicos de Tristerix no aportan información concluyente para apoyar una de las dos hipótesis relacionadas con los posibles grupos hermanos del género, ya que la ausencia de catafilos en los brotes de renuevo asocian Ligaria y Tristerix, en tanto que las inflorescencias terminales apoyan una relación cercana a Desmaria y Tupeia. Title in Spanish: Caracteres de la inflorescencia y las flores de ...

Floral anatomy of Tristerix longebracteatus (Loranthaceae)

“…The proposed coloration of the stamens, yellow in the filament and reddish in the anther (Kuijt, 1988), which are clearly observed in Contero and Dehesa (2007) for T. longebractatus specimens from Cayambe (Ecuador), contrasts with the reddish coloration of the filaments and yellow of the anthers in our material. Also, the pendant position of the inflorescences in González and Pabón (2017) contrasts with the erect position observed in this study. Kuijt (1988) described variation in leaf size and floral length across this species' broad geographic distribution, but it should be noted that the characters reported above are also variable.…”

“…This is consistent with the results obtained by Amico et al (2007) in whose phylogeny the three species make up a clade. Studies in the genus Tristerix have concentrated mainly on aspects such as morphology, phylogeny, biogeography and pollination, as in the recent work of González and Pabón (2017) where some floral and inflorescence characters were studied in relation to their ornithophyllous pollination.…”

“…Within the tribe Psittacantheae, the structure of the gynoecium presents variation, including: (1) trilocular ovaries with ategmic ovules in the genus Tripodanthus (Cocucci, 1983;Venturelli, 1983), (2) unilocular ovaries with a central conical structure called a mamelon or collective ovules in the genera Peristethium (Robles, Raz, & Marquínez, 2015), Pasovia (= Phthirusa; Kjuit, & Weberling, 1972) and Strutanthus (Venturelli, 1984a(Venturelli, , 1984b and (3) gynoecium formed by five congenitally fused carpels with a central solid ovary around a simple mamelon in Tristerix (González & Pabón, 2017).…”

“…(1) annular nectaries between the petals and style in species of the Psittacanthinae subtribe (for example in Peristethium, Robles et al, 2015), (2) stylar nectaries in Ligaria (Galetto, Bernardello, & Juliani, 1990;Kuijt, 1990) and (3) supraovary nectary disks in Tristerix spp. (González & Pabón, 2017).…”

“…Kuijt (1988) described variation in leaf size and floral length across this species' broad geographic distribution, but it should be noted that the characters reported above are also variable. González and Pabón (2017) indicate that in the Tristerix species that they studied, "five vascular bundles enter the base of the pedicel [….] above which they radially split into an outer ring of five traces that irrigate the common petal-stamen bases and an inner ring that serves the gynoecium."…”