Linaria alpina, the alpine toadflax, is a purple-flowered plant native to mountainous areas of southern and central Europe. It belongs to the family Plantaginaceae. It was first described by Carl Linnaeus, and given its current name by Philip Miller.
Etymology The generic name Linaria is derived from the Latin name for "resembling flax (linen)". It refers to the similarity of the leaves of some species in this genus to those of the common flax species, Linum usitatissimum. The specific epithet alpina indicates that the plant is of alpine origin or inhabits mountainous regions with habitats similar to alpine altitudes.
Taxonomy The family Plantaginaceae includes 12 tribes, 105 genera, and over 1,800 species. The genus Linaria belongs to the tribe Antirrhineae, which is composed of nearly 200 species distributed across North America, Europe, Africa, and Asia. Until recently, Linaria and related genera were included in the families Scrophulariaceae or Veronicaceae depending on the author. Modern APG classification places them within the Plantaginaceae. The scientific name of this species was initially described by Linnaeus (1707–1778) under its basionym Antirrhinum alpinum. It was later reclassified to its current name by the Scottish botanist Philip Miller (1691–1771) in the 1768 8th edition of his publication The Gardeners Dictionary.
Phylogeny Traditionally, the spontaneous species of the Italian flora are divided into four sections; Cymbalaria, Elatinoides, Linariastrum, and Chaenarrhinum. L. alpina is included in section Linariastrum, which is distinguished by sessile leaves with pinnate venation, flowers arranged in naked terminal racemes, and corollas with the throat completely obstructed by a prominent palate. More recent classifications have assigned the species to section Supinae. Current phylogenetic research indicates that species within the genus Linaria are distributed across six clades. L. alpina is located within the sixth clade, which, together with the fifth clade, forms a sister group representing the "core" of the genus. L. alpina and Linaria arenaria DC. form a sister group, although the seeds of the latter are crested rather than winged. The chromosome number of L. alpina is 2n = 12.
Description Linaria alpina is a hairless herb that can behave as an annual, a biennial, or a perennial. It reaches heights of 5–15 centimetres (2–6 in), though some specimens can reach up to 20 cm (8 in). Its primary biological form is a scapose hemicryptophyte, with overwintering buds at ground level protected by snow or litter, but it can also be a scapose therophyte, surviving via seed, or a rhizomatous geophyte, relying on underground rhizomes. The plant is almost always prostrate, lying flat with only the tips ascending, and possesses a thread-like, often creeping rhizome. The entire plant is glabrous (hairless) and glaucous (waxy grey-blue). As with many other members of the genus, Linaria alpina flowers have a blue-violet or pinkish corolla, with short spurs 8–10 mm long. The upper lip is deeply two-lobed, purple with two yellow-orange spots, and an orange throat lobes in the centre, creating a striking colour contrast and making it easily identifiable when in flower. This is likely an optical signal for insects.
Vegetative organs Roots: The root system tends to have a taproot. Stem: The aerial part of the stem is prostrate or ascending; its consistency is slender and fragile. An underground stem (rhizome type) may occasionally be present. Leaves: The fleshy leaves are linear to lanceolate, entire, and glaucous with a blue-green border. They measure roughly 5–20 mm long and 2–3 mm wide. Along the stem, they are subsessile and arranged in whorls of four, often becoming densely imbricate (overlapping) to form pseudo-rosettes at the apex of sterile branches. The upper leaves may transition to an alternate arrangement.
Inflorescence and flowers Three to fifteen flowers form a sparse, dense, or capitate raceme approximately 1 cm long. Individual flowers are pedunculate, with stalks are 2–4 mm during flowering, becoming straight and accrescent, 6–12 mm long, during fruiting. The flowers are hermaphroditic, zygomorphic, and tetramerous.
Floral formula: X or ∗ K ( 4 − 5 ) , [ C ( 4 ) or ( 2 + 3 ) , A 2 + 2 or 2 ] , G ( 2 ) , capsule {\displaystyle X{\text{ or }}*K_{(4-5)},[C_{(4){\text{ or }}(2+3)},A_{2+2{\text{ or }}2}],G_{(2)},{\text{capsule}}}
Calyx: The calyx is tubular-campanulate, more or less actinomorphic, and gamosepalous. It is formed by five deep, subequal laciniae (lobes) measuring 3–5 mm. Corolla: The corolla is gamopetalous, tubular, and personate (completely closed by a bulge of the upper lip). It measures 8–22 mm in total length. The posterior (upper) lip consists of two erect petals, while the anterior lip consists of three reflected petals. It is typically deep violet or pinkish with two striking orange patches on the lower lip. An abaxial spur (or sac) is present at the throat, measuring 6–7 mm in length. Androecium: The androecium is formed by four didynamous stamens (two long, two short), all of which are fertile. The filaments are adnate to the base of the corolla and are included or only slightly protruding. The anthers consist of two distinct, divaricate thecae that form a ring-like structure. Dehiscence is longitudinal, and the pollen grains are tricolporate. Nectar is located in the spur and is only accessible to insects strong enough to enter the closed throat. Gynoecium: The gynoecium is bicarpellary (syncarpous). The ovary is superior with axile placentation and ranges from ovoid to subglobose. The ovules per locule are numerous, have a single tegument, and are tenuinucellate (nucellus reduced to a few cells). The style has a stigma ranging from capitate to strongly bilobed.
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