Papaver - Phylogeny of Papaver and Related Genera

Phylogeny of Papaver and Related Genera

Papaver sect. Argemonidium includes four annual, half-rosette species, P. argemone, P. pavonium, P. apulum, and P. hybridum (Kadereit 1986a). Papaver apulum, P. argemone and P. pavonium occur allopatrically from the Adriatic Sea to the Himalayan range. P. hybridum is distributed widely from the Himalayas to Macaronesian Islands. These species are easily distinguished in petal and capsule characters, but are clearly closely related according to molecular analysis. Argemonidium is a sister group to all other Papaver sections, with characteristic indels. Morphological characters also support this distinction, including the presence of an apical plug in the capsules, long internodes above the basal leaf rosette, bristly capsules and polyporate pollen grains. Carolan et al. (2006) supported Kadereit et al. (1997)’s suggestions that Argemonidium and Roemeria are in fact sister taxa. They share some morphological characters that distinguish them from Papaver, including polyporate pollen grains, and long internodes superior the basal leaf rosette. Previous taxonomies of the Old World clade did include the close relationship between Argemonidium and Romeria, nor Argemonidium’s distinctness from Papaver s.s. Carolan suggest Argemonidium be elevated to genus status, with Romeria a sub-genus.

Papaver sect. Meconella is widely distributed, with populations spanning central, inner and eastern Asia, Siberia, Scandinavia, northern Greenland, Canada, the Rocky Mountains, and regions of Europe. It has been distinguished from other Papaver sections morphologically by its bristly, valvate capsules, pinnatisect leaves, pale stamen, and white, orange or yellow corolla. Older taxonomies divided Meconella into two groups based on degree of leaf dissection (finely dissected leaves vs. broad leaf lobes). Kadereit (1990) and Kadereit and Sytsma (1992) regarded finely dissected leaves as a derived character, and suggested that Meconella formed a group with Argemonidium as sister to other Papaver sects. Bittkau and Kadereit (2002) demonstrated that for P. alpinum s.l. broad leaf lobes were ancestral. Carolan et al. (2006) resolved Meconopsis as sister to sect. Meconella, forming a sister clade to the rest of Papaver, excluding Argemonidium. Meconella possesses a sessile stigmatic disc, similar to the typical discs of Papaver sect. Papaver., yet differences in the disc and other morphological characters have led to suggestions that this feature may not be homologous. The results of the Carolan et al. (2006) analysis present a major problem to previous taxonomy of the genera Meconopsis, and Papaver. As several species of Meconopsis (excluding M. cambrica) and P. Meconella resolved as a monophyletic group, sister to other Papaver sects., either Meconella must be elevated to genus status, or combined with the Asian species of Meconopsis, as a subgenus of Papaver.

Papaver sects. Californicum and Horrida have unique geographic distributions in relation to the rest of the genus. Horrida is represented by a single species Papaver aculeatum of, an annual flower native to South Africa. The capsule is glabrous narrow, long and poricidal. The vegetative parts are covered with setae, and the growth form is a rosette with rarely branching axes, and narrowly elliptical incised leaves. P. sect. californicum, is also represented by a single annual species, of the same name. As the name implies, it is native to western North America, and is characterized by a slender, ribbed, glabrous capsule, a racemose inforescence, yellow anthers and filaments, and valvate capsule dehiscece. Previous morphological-based taxonomies of these species have led to unreliable groupings. Horrida and Pilosa have recemose inforescences, pale filiform filaments and long capsules with flat stigmatic discs, while P. californicum and sect. Meconidium share valvate capsule dehiscence and pale filaments, but geographically these species are distinct, and do not follow molecular evidence. Commonality among these features is therefor hypothesized to be a result of convergence. In Carolan et al.’s (2006) combined ITS, trnL-F trees, both Horrida and Californicum attach to basal nodes within the main clade Papaver. Kadereit et al. (1997) postulated that Stylomecon heterophylla arose from within Papaver and should not be relegated as a separate genus. S. heterophylla and P. californicum are both native to southwestern North America, and share habitats. They are also morphologically similar, sharing glabrous buds, bright orange corollas, and yellow anthers. Their capsules are different, with S. heterophylla possessing a distinct style that is reminiscent of those in many Meconopsis species. However, Carolan et al.’s (2006) analysis strongly supports a monophyletic group for S. heterophylla and P. californicum, sister to the core Papaver sects, with Horrida, basal to that grouping. They recommended that both sects. Californicum and Horrida be elevated to “subgenera” within Papaver. The authors reject the genus status of Stylomecon.

Meconopsis is composed of mostly Asian dwelling species, and a single European representative, M. cambrica. Kadereit et al. (1997) first provided evidence that this relationship is not monophyletic. Carolan et al. (2006) confirmed the separation of M. cambrica from the rest of Meconopsis. In fact, it forms a well-supported sister-group to the core sections of Papaver, excluding Argemonidium, Californicum, Horrida and Meconella.

The core sections of Papaver s.s. form a well-supported clade, consisting of Pseudopilosa, Pilosa, Papaver, Carinatae, Meconidium, Oxytona, and Rhoeadium. Pseudopilosa spp. have a subscapose growth habit, and their distribution includes south-western Asia, northern Africa and southern Spain. There are some leaves on the lower part of the flower axis carrying a single flower. Carolan et al.’s (2006) analysis placed Pseudopilosa as sister to the remaining Papaver s.s. sections. Pilosa is a single species, P. pilosum, found mostly in western Turkey Sects. Pilosa and Pseudopilosa are separated based on morphological and chemical differences.

The monophyly of Carinatae, Papaver and Rhoeadium is questionable based on current molecular evidence. Papaver sect. Rhoeadium comprises seventeen annual species. Carolan et al. (2006) use three representative species, P. commutatum, P. dubium, and P. Rhoeas for their genetic analysis. The geographic center of Rhoeadium’s diversity is in south-western Asia and the Aegean area. They have porocidal capsules and usually dark filaments. This section is morphologically diverse however, leading Kadereit (1989) to recognize three distinct groups. The first comprises species with tetraploid and hexaploid genomes, with long capsules. The second group contains diploid species and diverse morphologies. The third group consists of diploid species and uniform morphologies. Carolan et al. (2006) showed some incongruences between their trnL-F and ITS maximum parsimony trees, showing weak support for Kadereit’s (1989) groupings. Further analyses with more species and more samples will be necessary to resolve the phylogeny at this level.

Papaver has traditionally been characterized by the absence of a stigma, and the presence of a sessile stigmatic disc. Carolan et al. (2006) demonstrated that several species with this trait however are closely related to taxa possessing a style e.g. S. heterophylla and P. californicum, and P. sect. Meconella and Asian Meconopsis. This evidence, in combination with morphological differences among the discs suggests convergent evolutionary pathways. Papaver has long been considered the most derived clade within Papaveroideae, due to the belief that the stigmatic disc was an apomorphous characteristic. Sections Meconella and Californicum exhibit valvate dehiscence, and their basal position within Papaver suggest this may be an ancestral form. Its presence in Meconidium, however, suggests it is also a synapomorphy within that group.

Section Note: Meconella (not to be confused with the genus Meconella) has an alpine and circumpolar arctic distribution and includes some of the most northerly-growing vascular land plants.