Floral anatomy of Thomandersia (Lamiales), with particular reference to the nature of the retinaculum and extranuptial nectaries

Abstract

Thomandersia is an isolated genus that is currently unplaced in Lamiales. In the past it has been classified in Acanthaceae or Pedaliaceae, on the basis of intuitive assessments of a limited number of morphological characters. Recent molecular sequenced-based phylogenies have suggested a relationship to Bignoniaceae, Schlegeliaceae or Verbenaceae. Here we present new observations of the floral anatomy of Thomandersia , with particular emphasis on the structure of the retinaculum, a character shared with Acanthaceae, and calyx nectaries, which may be shared with other families in Lamiales. The morphological and anatomical characters of Thomandersia are discussed in the context of recent phylogenetic hypotheses for Lamiales, with the aim of identifying potential primary and secondary homologies between Thomandersia and related families in Lamiales. We find that Thomandersia shares a range of characters with each of the families to which it might be sister-group, and that some of these primary homologies must therefore be homoplastic. In particular, if the topology based on molecular sequence data is correct, the retinacula of Thomandersia and Acanthaceae are homoplastic and represent an example of parallel morphological evolution.

Gyroscopic stabilization minimizes drag on Ruellia ciliatiflora seeds

“…Fruits of R. ciliatiflora explosively dehisce on contact with water (i.e. are hygrochastic) to launch seeds from internal retinacula, or jaculators, which are small woody hooks that cradle seeds [14] and facilitate their dispersal [10] (figure 1b). Each retinaculum has a small groove to cradle and guide the launch of its seed, and as a fruit splits downward along the vertical seam connecting the two valves, the retinacula accelerate the seeds with contact forces applied slightly below the seeds' centre of mass (figure 1b; electronic supplementary material, video S1).…”

Anatomía floral de los géneros del complejo Milla (Themidaceae)

“…Además varios autores indican que los fi lamentos están connados en los miembros del complejo, pero su tamaño y forma difi ere (Lenz, 1971;López-Ferrari y Espejo, 1992;Turner, 1993) o se ha generalizado sobre la adnación de la base del ovario con el tubo fl oral para todos sus miembros (Pires y Sytsma, 2002). A la fecha, existen varias interrogantes sobre los tamaños, grados de adnación y connación de los diferentes verticilos y la presencia y características del ginóforo para los géneros de este complejo, en particular para las cuatro especies de Dandya. La utilidad de los caracteres anatómicos de la fl or en la circunscripción en el nivel de familia y en la delimitación de géneros es ampliamente reconocida (Mogensen, 1969;Lenz, 1976;Fallen, 1985;Berg, 1996Berg, y 2003Endress, 1996;González & Rudall, 2003;Rudall, 2003;Rudall et al, 2003;Strange et al, 2004;Rudall et al, 2005;Wortley et al, 2005;Martínez-Cabrera, 2007;Sajo et al, 2010). Por tal motivo, se describe la anatomía fl oral de los seis géneros del complejo Milla sensu Gándara et al (2009) con el propósito de: (1) confi rmar si las especies de Dandya presentan ginóforo, (2) comparar las características del ginóforo de los géneros del complejo Milla, (3) identifi car si existen caracteres de la anatomía fl oral exclusivos o compartidos entre los géneros del complejo y (4) examinar algunos rasgos fl orales a la luz de la fi logenia más reciente del complejo Milla.…”

Morphological and ontogenetic studies with inflorescences and flowers of Lepidagathis Willd. (Acanthaceae)

“…An opposite case, the segregation of Thomandersia Baill from Acanthaceae, was supported by studies with the fruits development. Wortley et al (2005) verified that the retinacula from the Thomandersia fruits are homoplastic to those characteristic of the Acanthoideae subfamily, presenting an example of parallel evolution within the Lamiales. Therefore, the genus was elevated to the rank of family, as Thomandersiaceae Sreem.…”

“…Only recently the origin and nature of reproductive structures have been investigated, like the retinacula of Thomandersia (a genus elevated to the rank of family), and the structure of the flowers of Thunbergioideae and Avicennia (which are part of Acanthaceae s.l. and show different floral morphologies from those of Acanthaceae s.s.) (Wortley et al, 2005;Borg and Schönenberger, 2011). This new information provided by an anatomical approach emphasizes the importance of ontogenetic studies to understand the evolution, development, and relations amongst the family.…”

“…Another common feature of these plants is the spike or thyrse inflorescence, made by decussate conspicuous bracts and a pair of bracteoles before each flower (Braz et al 2002, Souza & Lorenzi 2012. Other frequent morphological aspects are the presence of cystoliths on vegetative organs (Solereder 1908 and the presence of a retinacula (lignified funicule) sustaining the seeds on the explosive capsules (Tieghem 1908, Wortley et al 2005. Both are key features that help identify subfamilies and tribes (Scotland & Vollesen 2000.…”