Comprehensive characteristics and genetic diversity of the endemic Australian Viola banksii (section Erpetion, Violaceae)

Abstract

Viola banksii, the type species of section Erpetion, is endemic in eastern mainland Australia. In this paper we characterise morphological and anatomical features and assess genome size and genetic diversity in combination with the breeding system. V. banksii develops exclusively chasmogamous flowers. Ovules are anatropous, crassinucellate and bitegmic, the female gametophyte is of the Polygonum type, and the embryo is of Asterad type surrounded by nuclear endosperm. Pollen is non-heteromorphic, 3-aperturate, and highly viable. V. banksii grows in shade on moist, well drained, often sandy soils, and this is reflected in the anatomy of its organs, which includes a lack of subepidermal collenchyma in aerial parts, large leaf epidermal cells with thin cell walls, a narrow cuticle layer, and vascular bundles with xylem that are not rich in vessels. V. banksii is tolerant to zinc and lead based on phytotoxicity test. The high chromosome number (2n = 10x = 50) does not correspond to a small genome size (2C DNA = 1.27 pg). Low mean intra-populational gene diversity (HS = 0.077) detected by ISSR markers confirms the strong influence of selfing and clonal propagation by pseudostolons. Unique morphological traits of V. banksii include nyctinastic petal movement, the lack of a floral spur, the presence of gland-like protuberances on two stamens, and the presence of pseudostolons, which could be a synapomorphy for the whole section.

A revised phylogenetic classification forViola(Violaceae)

“…Both homoeolog number and chromosome count for sect. Erpetion indicate that this lineage is allo-octoploid (Figure 4); the recent count of 2n = 50 in V. banksii [98] is very close indeed to the expected 2n = 48 based on x = 6 in the diploid ancestor of sects. Chamaemelanium and Rubellium.…”

“…Borealiamericanae in North America [67,172,183], sect. Erpetion in Australia [98,[184][185][186][187], as well as the genus as a whole in China [76,78]. The last remaining blank spot seems to be the southeastern Asian and Malayan species, which comprises relatively few, but morphologically specialised and probably not closely related species that do not fit seamlessly with the taxonomic system, as indicated by the few treatments available [74,[188][189][190][191].…”

“…There is no indication that this ancestral tetraploid Erpetion still exists. Section Erpetion is characterised karyologically by the secondary base chromosome number x’ = 25 [98]. The estimate of 10 x for sect.…”

Seasonal and Simultaneous Cleistogamy in Rostrate Violets (Viola, subsect. Rostratae, Violaceae)

“…Our results documented constant differences between CH and CL flowers at different stages of their development and at fruiting, allowing for the easy recognition of fruits derived from CH or CL flowers. CH flowers attract insect pollinators and promote cross-pollination and potential genetic diversity within populations [ 34 , 35 , 36 , 37 , 38 , 39 , 40 ]. In contrast, obligate self-pollinated CL flowers produce pure lines.…”

“…The anatomy of V. reichenbachiana stem, peduncle, petiole and CL flowers was analyzed on acetocarmine-stained handmade cross-sections as well as on microtome-made paraffin cross-sections stained with Heidenhain’s hematoxylin combined with Alcian blue according to the procedure described in [ 39 ].…”