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The Viola epipsila-V. palustris complex is a highly taxonomically complicated group of species in its entire circumboreal range of distribution. Habitat loss, forest flooding, and hybridization could lead to the extinction of V. epipsila. A hybrid index and principal component analysis (PCA) were used to select qualitative and quantitative morphological features to distinguish parent species and hybrids, inter simple sequence repeat (ISSR) markers to determine the genetic diversity of the populations, flow cytometry to estimate the genome size (GS), and non-coding chloroplast DNA (cpDNA) regions to indicate the directions of crosses. All taxa are very morphologically variable, and their features can change within a season. The most stable feature is the distance of the bracts on the pedicel from the rhizome. The genetic diversity of all taxa populations is low and highly influenced by selfing and vegetative propagation. The population structure is differentiated: populations of V. epipsila or V. palustris, mixed populations with both parent species, F1 hybrids and populations with introgressive forms occur in different regions. The interspecific GS variation corresponds to the ploidy level (4x = 2.52 pg, 8x = 4.26 pg, 6x = 3.42 pg). Viola epipsila is the mother plant of the hybrids. Research has shown the risk of V. epipsila extinction in Central Europe and the importance of local populations in studying the role of hybridization in reducing/maintaining/increasing biodiversity. [ABSTRACT FROM AUTHOR]

Highlights • Discovery of a new pollination systems not described elsewhere in the genus Viola. • Temporal flower closure (nyctinasty) provides self- and cross-pollination realized by a single flower. • The timing of nyctinastic movements is correlated with stigma receptivity. • Floral characters indicate that V. banksii may have a pollination deceit strategy. • Temporal flower closure seems to be endogenous but affected by changes from light to darkness. Abstract Viola banksii of the eastern Australian and Tasmanian sect. Erpetion produces exclusively chasmogamous flowers, unlike most other temperate taxa of Viola which additionally produce obligatory self-pollinated cleistogamous flowers. This study explored flower structure and nyctinastic flower movements (temporal flower closure), the correlation of the timing of nyctinastic movements with stigma receptivity, and self-compatibility of flowers. Petal movement in day/night cycles was documented by two cameras. Floral morphology, anther protuberance anatomy, stigma receptivity, and pollen tube growth were examined using scanning electron microscopy, fluorescent microscopy, histochemical and sectioning techniques. Diurnal petal movements that cause flowers to be open during the day and closed during the night were documented in V. banksii. Chasmogamous flower colour, fragrance, anterior petal venation, and the indurated green area at the base of the anterior petal are all likely to play roles for pollinator attraction. Unlike most other Viola species, the anther protuberances do not function as nectaries. The flowers offer pollinators no nectar reward. The short time of stigma receptivity (2–3 days) of individual flowers limits opportunities for insect visitation and cross-pollination. Night-closed flowers of V. banksii appear to facilitate self-pollination. Self-compatibility was confirmed by tracking the pollen tube growth from the stigma to the ovule in spontaneous and hand self-pollinated flowers. Over the floral phenological cycle, nyctinasty coincides in time with stigma receptivity and, hence, the ability of self-pollination. We discovered that the same chasmogamous flower of V. banksii can cross-pollinate while open during the day, but self-pollinate while closed during the night (i.e. acting as a cleistogamous-like flower). Several floral characters indicate that V. banksii exhibits a pollination deceit strategy. Such a pollination system has not been described elsewhere in Viola. [ABSTRACT FROM AUTHOR]

• Micropropagation combined with cryopreservation delivers an efficent ex situ conservation toolbox for V. stagnina. • Cryoprotection does not affect genome size, it generates low genetic diversity of post-thaw recovered plants. • The studies may be helpful in conservation of the other rare and threatened plant species as well. The use of cryopreservation techniques for plant species confined to wet habitats is difficult to standardize due to low tolerance for dehydration of plant tissue. The study aimed to develop a procedure for the long-term storage in liquid nitrogen (LN) of Viola stagnina , a rare and endangered species of moist habitats whose European range is constantly decreasing. Adventitious shoot apices of different sizes (small, medium and large) were cryopreserved using encapsulation/dehydration, encapsulation/vitrification (in PVS2 or PVS3 solutions) and droplet/vitrification methods. Encapsulation/dehydration was the most efficient technique, and 47.7 % regrowth was obtained with an average rate of shoot regeneration of 2.4 %. Less than 27.6 % of cryopreserved shoot apices were able to produce shoots with an efficiency of 0.35 or less based on vitrification procedures. In post-thaw recovery culture, adventitious shoots were produced indirectly (via callus). The genetic variation among recovered shoots after different cryopreservation methods was low (Dice coefficient not exceeded 0.09). Some clones were genetically uniform with the mother plant estimated by ISSR molecular markers. The genome size of all post-thaw recovered regenerants, except one individual with a multiplicated genome, was uniform with the initial plant. This paper presents the first report on cryopreservation of V. stagnina with a developed protocol that can be used in ex situ conservation of the species. [ABSTRACT FROM AUTHOR]