Systematics of “horned” dodders: phylogenetic relationships, taxonomy, and two new species within the Cuscuta chapalana complex (Convolvulaceae)

Abstract

The Cuscuta chapalana complex (Convolvulaceae) is a recently circumscribed clade within the subgenus Grammica that includes several little-known species from Mexico and Central and northern South America characterized by the presence of peculiar subapical multicelullar appendages on the corolla and often on the calyx lobes. Basic morphology, scanning electron microscopy, and DNA sequence data from the plastid trnL-F region and the 26S rDNA and internal transcribed spacer nuclear regions were used to investigate the phylogenetic relationships within the group and to test the species limits. Multicellular appendages are horn-like or tubular in shape and bear one or more stomata at their tips; hence the vernacular name "horned" dodders. Eight lineages were reconstructed; two of them, both from Mexico, were described as new species: Cuscuta bonafortunae Costea & I. García, sp. nov., and Cuscuta carnosa Costea & Stefanović, sp. nov. Cuscuta pringlei is redefined as a variety of Cuscuta strobilacea. A taxonomic treatment with an identification key, descriptions, and illustrations is provided. Résumé : Le complexe Cuscuta chapalana (Convolvulaceae) constitue un clade récemment circonscrit récement circonscrit dedans le sous-genre Grammica incluant plusieurs espèces peu connues du Mexique, du centre et du nord de l'Amérique du Sud, caractérisées par la présence d'appendices subapicales multicellulaires particulières sur la corolle, et souvent sur les lobes du calice. A fin d'examiner les relations phylogénétiques dans ce groupe et vérifier les limites des espèces, les auteurs ont utilisé les données morphologiques générales, la microscopie électronique à balayage et les séquences de l'ADN provenant de la région plastidique trnL-F et des régions nucléaires de 26S rADN et de l'espaceur interne transcrit (ITS). Les appendices multicellulaires prennent la forme d'une corne ou d'un tube, et portent un ou plusieurs stomates à leur apex, d'où le nom vernaculaire de cuscute cornue. Ils ont reconstruit huit lignées; ils décrivent deux d'entre elles, toutes deux du Mexique, comme espèces nouvelles : Cuscuta bonafortunae Costea & I. García, sp. nov. et Cuscuta carnosa Costea & Stefanović, sp. nov. On redéfinit le Cuscuta pringlei comme une variété du Cuscuta strobilacea. Les auteurs fournissent un traitement taxonomique avec une clé d'identification, des descriptions et des illustrations.

Plastid genome evolution across the genus Cuscuta (Convolvulaceae): two clades within subgenus Grammica exhibit extensive gene loss

“…Subgenus Grammica , the largest and most diverse lineage of Cuscuta , is represented by 93 species (124 accessions), with multiple samples from each of 15 clades (A–O) circumscribed in Stefanović et al (2007). In particular, sampling was concentrated extensively on clades ‘K’ and ‘O’, two groups in which the presence of plastomes has been previously questioned (van der Kooij et al, 2000; McNeal et al, 2007a; Stefanović et al, 2007; Costea et al, 2011). The three remaining subgenera were also sampled in proportion to their diversity: four species from ‘ Pachystigma ’, eight from subgenus Cuscuta , and seven from subgenus Monogynella .…”

Diversity, evolution, and function of stomata bearing structures in Cuscuta (dodders, Convolvulaceae): From extrafloral nectar secretion to transpiration in arid conditions

“…The fine morphology of SPs is quite unique in many species (Fig. S2I-T), which makes these structures useful in species delimitation as proven by several recent taxonomic revisions (Costea and Stefanović, 2009;Costea et al, 2011aCostea et al, ,b, 2013.…”

“…Field determinations were conducted in Mexico, Abadiano, Michoacan (19 • 59 45.18 N, 102 • 51 41.04 W) using a natural population of C. costaricensis, a species with SPs both on the haustorial stems and perianth (Costea et al, 2011a), and its preferred host, Tithonia tubiformis. The xylem and phloem of both parasite and host are connected by the parasite's haustoria, which transfer unidirectionally the water and nutrients to the parasite (Stewart and Press, 1990;Lambers et al, 2008).…”

“…To complicate things further, non-secretory multicellular structures with stomata, similar morphologically to Mirande's stem SPs, were recently described on the flowers of several new species that belong to subg. Grammica (Costea and Stefanović, 2009;Costea et al, 2011aCostea et al, ,b, 2013.…”

“…This would be particularly intriguing because, in general, holoparasitic plants possess low stoma densities and very reduced water loss (Raven, 1983;Seel et al, 1992;Dawson et al, 1994;Ehleringer and Marshall, 1995;Heide-Jørgensen, 2008). If the transpiration role is confirmed, it would also be interesting to explore some of the ecophysiological implications because all the recently described species with floral SPs are apparently confined to arid areas (Costea and Stefanović, 2009;Costea et al, 2011aCostea et al, ,b, 2013, and a water loss in such conditions would be more than unusual.…”