Molecular phylogenetic species delimitation in the aquatic genus Ottelia (Hydrocharitaceae) reveals cryptic diversity within a widespread species.

Ottelia, a pantropical genus of aquatic plants belonging to the family Hydrocharitaceae, includes several narrowly distributed taxa in Asia. Although the Asian species have received comparatively more research attention than congeners in other areas, various key taxonomic questions remain unaddressed, especially with regards to apparent cryptic diversity within O. alismoides, a widespread species complex native to Asia, northern Australia and tropical Africa. Here we test taxonomic concepts and evaluate species boundaries using a phylogenetic framework. We sampled five of the seven species of Ottelia in Asia as well as each species endemic to Africa and Australia; multiple samples of O. alismoides were obtained from across Asia. Phylogenetic trees based on five plastid DNA markers and the nuclear ITS region shared almost identical topologies. A Bayesian coalescent method of species delimitation using the multi-locus data set discerned one species in Africa, one in Australia and four in Asia with the highest probability. The results lead us to infer that a population sampled in Thailand represents a hitherto unrecognised cryptic taxon within the widespread species complex, although the apparent lack of unambiguous diagnostic characters currently precludes formal description. Conversely, no molecular evidence for distinguishing O. cordata and O. emersa was obtained, and so the latter is synonymised under the former. Two accessions that exhibit inconsistent positions among our phylogenetic trees may represent cases of chloroplast capture, however incomplete lineage sorting or polyploidy are alternative hypotheses that ought to be tested using other molecular markers.

Calla palustris (Araceae): New palynological insights with special regard to its controversial systematic position and to closely related genera.

Almost all systematic treatments agree that Calla is a puzzling case, being a highly autapomorphic taxon with obscure relationships. In molecular-based classifications the variable placements of Calla within Aroideae conflict strongly with those in morphologically and anatomically based systematic classifications, which treat the genus as a subfamily (Calloideae) of its own. We studied the pollen morphology and ultrastructure of Calla by light and electron microscopy, and mapped the relevant pollen characters as well as some flower characters to the proposed placements of Calla within the Araceae as indicated in the various molecular phylogenies. Calla pollen is extraordinary within the entire Araceae. Pollen grains are small, and basically disulcate or with a ring-like aperture. The ornamentation is psilate to perforate, and the pollen wall consists of a sporopolleninous tectate-columellate exine. These pollen characters are shared with those of several earlier-diverging aroid taxa, especially with those of subfamily Zamioculcadoideae, whereas pollen characters in members of subfamily Aroideae deviate significantly. These findings are in accordance with other floral characters. Therefore, we propose that Calla is best placed in a transition zone between either subfamily Zamioculcadoideae (Stylochaeton clade) and subfamily Aroideae (Aroideae clade) or between subfamily Zamioculcadoideae (Stylochaeton clade) and subfamily Lasioideae.

Relationships within the Araceae: comparison of morphological patterns with molecular phylogenies.

PREMISE OF THE STUDY: The first family-wide molecular phylogeny of the Araceae, a family of about 3800 published species in 120 genera, became available in 1995, followed by a cladistic analysis of morpho-anatomical data in 1997. The most recent and comprehensive family-wide molecular phylogeny was published in 2008 and included species from 102 genera. We reanalyzed the molecular data with a more complete genus sampling and compared the resulting phylogeny with morphological and anatomical data, with a view to contributing to a new formal classification of the Araceae. METHODS: We analyzed 113 aroid genera and 4494 aligned nucleotides that resulted from adding 11 genera to the 2008 molecular matrix. We also analyzed 81 morphological characters in the context of the molecular phylogeny, using an extended version of the 1997 morpho-anatomical data set. KEY RESULTS: The resulting maximum-likelihood phylogeny is well resolved and supported, and most of the 44 larger clades also have morphological or anatomical synapomorphies as well as ecological or geographic cohesion. Of the 44 clades, 16 are here newly circumscribed and informally named. However, some relationships remain poorly supported within the Aroideae subfamily. The most problematic placement is Calla within Aroideae, which conflicts with the distribution of morphological, anatomical, and palynological character states. CONCLUSIONS: The comparison of the molecular analysis with morphological and anatomical data presented here represents an important basis for a new formal classification for the Araceae and for the understanding of the evolution of this ancient family, a monocot group known in the fossil record from the early Cretaceous.

Phylogenetic relationships of aroids and duckweeds (Araceae) inferred from coding and noncoding plastid DNA.

Familial, subfamilial, and tribal monophyly and relationships of aroids and duckweeds were assessed by parsimony and Bayesian phylogenetic analyses of five regions of coding (rbcL, matK) and noncoding plastid DNA (partial trnK intron, trnL intron, trnL-trnF spacer) for exemplars of nearly all aroid and duckweed genera. Our analyses confirm the position of Lemna and its allies (formerly Lemnaceae) within Araceae as the well-supported sister group of all aroids except Gymnostachydoideae and Orontioideae. The last two subfamilies form the sister clade of the rest of the family. Monophyly of subfamilies Orontioideae, Pothoideae, Monsteroideae, and Lasioideae is supported, but Aroideae are paraphyletic if Calla is maintained in its own subfamily (Calloideae). Our results suggest expansion of the recently proposed subfamily Zamioculcadoideae (Zamioculcas, Gonatopus) to include Stylochaeton and identify problems in the current delimitation of tribes Anadendreae, Heteropsideae, and Monstereae (Monsteroideae), Caladieae/Zomicarpeae, and Colocasieae (Aroideae). Canalization of traits of the spathe and spadix considered typical of Araceae evolved after the split of Gymnostachydoideae, Orontioideae, and Lemnoideae. An association with aquatic habitats is a plesiomorphic attribute in Araceae, occurring in the helophytic Orontioideae and free-floating Lemnoideae, but evolving independently in various derived aroid lineages including free-floating Pistia (Aroideae).