Veronica pulvinaris
Veronica pulvinaris, one of the cushion snow hebes, is a species of flowering plant in the family Plantaginaceae. It is endemic to high elevation habitats of the mountains of the northern and central South Island of New Zealand, mostly east of the main divide. Joseph Dalton Hooker described Pygmea pulvinaris in 1864, which was transferred to the genus Veronica in 1906 by Thomas Cheeseman. Plants of this species are dioecious cushions with small, spirally imbricate, sessile leaves that have sparsely but evenly distributed hairs mostly on the upper half of the leaf surfaces and edges. They also have regular flowers with white tubular corollas with 5 petals and 2 stamens, and both the ovary and capsule have a dense covering of hairs at the apex. The conservation status of V. pulvinaris is not threatened. It is closely related to other snow hebe species, especially the other cushions, V. thomsonii, V. chionohebe and ''V. ciliolata.''
Taxonomy
Veronica pulvinaris is in the plant family Plantaginaceae. Joseph Dalton Hooker described Pygmea pulvinaris in Volume I of his Handbook of the New Zealand Flora in 1864. The species was transferred to the genus Veronica in 1906 by Thomas Cheeseman. Barbara Briggs treated the species as Chionohebe pulvinaris in 1976, but since 2007 it has been recognised as Veronica pulvinaris by many botanists in a more broadly circumscribed Veronica.The type specimen was collected on the summit of Mt Torlesse, Canterbury, by Julius von Haast in 1860–1. The holotype is at the herbarium at Royal Botanical Gardens Kew.
V. pulvinaris is one of four cushion plants and six other small herbs or subshrubs in the snow hebe lineage. The distribution and location of hairs are important characters in distinguishing V. pulvinaris from other snow hebe species. Veronica pulvinaris is characterised by the tips of its ovary and capsule having densely distributed hairs, as well as the leaf surfaces and edges having evenly and sparsely distributed hairs on the upper half.
Description
Veronica pulvinaris plants are perennial cushions with a woody base. Branches are multiple, erect, up to 39 mm long and 4.6 mm wide, and glabrous. Leaves are spirally imbricate, tightly or loosely appressed, sessile, 1.8–4.9 mm long by 0.6–1.8 mm wide, usually oblanceolate, narrowly obovate or spathulate, widest above the middle, usually with an obtuse apex, and entire. The leaf hairs are unicellular, non-glandular, appressed and up to 1.4 mm long. The inner leaf surface is usually sparsely hairy on the upper half, or rarely glabrous. The outer leaf surface is usually glabrous. Leaf edges are ciliate mostly on the upper half. Flowers are sessile, solitary and axillary near branch tips, with two bracts. Bracts are 2.2–4.1 mm long and 0.3–0.8 mm wide with an obtuse apex and hairs similar to the leaves but shorter. The calyx is 2.1–4.7 mm long, regular, with all lobes divided to the base of the calyx, hairy on the outside and lobe edges and glabrous on the inside. The corolla is 2.6–7.7 mm long, subregular and white. The corolla lobes are 1.0–2.4 mm long, spreading to erect, narrowly to very broadly obovate. There are 2 stamens, with white filaments 0.2–0.8 mm long and anthers 0.5–1.4 mm long. The style is 2.3–7.0 mm long, exserted, with a capitate stigma. The ovary is 0.5–1.1 mm long and densely hairy at the tip with hairs up to 0.4 mm long. Fruits are capsules with septicidal and loculicidal dehiscence, 1.0–3.0 mm long and 1.2–2.7 mm wide, hairy at the tip. There are up to 11 seeds in each capsule, and seeds are 0.5–0.9 mm long and 0.4–0.6 mm wide, discoid, and smooth.Veronica pulvinaris flowers from November to February and fruits mainly in December and January.
The chromosome number of Veronica pulvinaris is 2n = 42.
Distribution and habitat
Veronica pulvinars is endemic to the South Island of New Zealand, including northwest Nelson, Marlborough, Canterbury and possibly Otago, mostly on the eastern side of the main divide. Plants of this species can be found from 600 to 2260 m above sea level in alpine cushion herbfield or fellfield, usually in rocky areas including bluffs, crevices, stones and scree.Breeding system and seed dispersal
Like all other cushion snow hebes, Veronica pulvinaris is functionally gender dimorphic. This means individual plants are either male or female, and outcrossing between plants is required to produce seed. The flowers are insect pollinated.Regarding seed dispersal, V. pulvinaris uses hygrochasy, which is also known as the "splash cup" method. Thus, the fruiting capsule opens upon exposure to water, and then falling raindrops splash the seeds out of the open capsule.
Biochemistry
The water-soluble compounds that were isolated and identified from V. pulvinaris and another snow hebe species, V. thomsonii, showed that the iridoid chemical profile of these species was different from other New Zealand Veronica species, and more similar to high-elevation species of Veronica from the northern hemisphere. The authors of that study hypothesized that the similar chemical profiles were the result of convergent or parallel evolution due to their similar alpine habitats. In addition, there were some unique compounds that could differentiate V. pulvinaris and V. thomsonii from one another, as well as the two sampled populations of V. pulvinars from the Black Birch Range and Mt Arthur''.''Phylogeny
Multiple phylogenetic analyses have included multiple New Zealand species of Veronica, including Veronica pulvinaris and other snow hebes, to understand the phylogenetic history of the genus by analysing morphological data and standard DNA sequencing markers such as the internal transcribed spacer region, chloroplast DNA, nuclear low-copy DNA, and phylogenomics. Broadly speaking, these studies included one or few individuals of V. pulvinaris and the other snow hebe species, showing that they are highly supported within the southern hemisphere lineage of Veronica. In addition, V. pulvinaris is most closely related to the other cushion snow hebe species, V. thomsonii, V. chionohebe and V. ciliolata, followed by a sub-shrub snow hebe, V. densifolia, and sometimes also one or more of the remaining snow hebes that have been sampled in phylogenetic studies, including V. trifida, V. planopetiolata, or V. spectabilis.Another study that sampled multiple individuals and populations used chloroplast DNA and amplified fragment length polymorphisms to understand the phylogeography, species relationships and phylogeny of the snow hebes as a group. Veronica pulvinaris was highly supported as monophyletic based on AFLP data, and there was geographic structuring within the species. The chloroplast data, on the other had, showed widespread chloroplast haplotype sharing among the cushion snow hebes V. pulvinaris, V. thomsonii, V. chionohebe and V. ciliolata.
Two individuals of V. pulvinaris were included in a study that used Veronica transcriptomes to develop and validate new sequencing markers for the genus.