- Name also: Narrow-leaved Hawk’s-beard, Wall Hawk’s-beard
- Family: Daisy Family – Compositae, subfamily Cichorioideae (formerly Chicory Family – Cichoriaceae)
- Growing form: Annual or biennial herb.
- Height: 10–40 cm (4–15 in.). Upper stem often abundantly branched, more-or-less glabrous, leafy. Containing milky latex.
- Flower: Single flower-like capitula 1–2 cm (0.4–0.8 in.) broad, surrounded by involucral bracts. Capitulum flowers pale yellow, tongue-like, tip 5-toothed. Stamens 5. Gynoecium composed of 2 fused carpels. Involucral bracts in 2 rows, outer bracts short, spreading, often different lengths, inner bracts much longer, equal length, almost linear, often with glandular hairs, sometimes blackish (ssp. nigrescens). Capitula borne in a corymbose cluster or only several large capitula (ssp. nigrescens).
- Leaves: In basal rosette and alternate on stem. Rosette leaves prostrate, soon withering. Lowest stem leaves stalked, upper stalkless, slightly amplexicaul. Blade lanceolate–almost linear, with sagittate base, almost glabrous, lower leaves irregularly large-toothed–narrowly lobed, upper leaves more-or-less toothless–with sparsely toothed margins with revolute margins.
- Fruit: Flat, low-ridged, reddish brownish violet achene, crowned with white unbranched hairs.
- Habitat: Open rocky outcrops, precipices, dry meadows, sandy fields, fallow fields, gravel pits, wasteland, roadsides, railway yards.
- Flowering time: June–September.
- Endangerment: Ssp. nigrescens is endangered and protected in all of Finland.
Narrowleaf hawksbeard’s original stand in Finland is native to nutritious rocky outcrops, bird rocks and meadows, but the alien stand which thrives close to people is much more common. It probably originally became common through cereal cultivation – it can still be seen now and then growing in fields as a weed – but it is more common in fallow fields and beside roads. In particular it thrives around inhabited areas which people have made more fertile. In an urban environment the species has made use of open, dry places in railway yards, industrial and storage areas, waste ground and cracks in the pavement. It used to even grow on lichenous turf and shingle roofs. Narrowleaf hawksbeard’s capitula open soon after sunrise but they close before noon. It is pollinated by flies, butterflies and hymenopterans. Its abundance varies greatly from year to year: a dry spring will exhaust the plants and stands become rare. Part of the seed-bank remains intact in the soil, however, ready to grow in a more favourable, damp spring.
Like many annual species, narrowleaf hawksbeard is very diverse. Apart from the type species (ssp. tectorum), the very rare and protected subspecies nigrescens also grows in eastern Finland. It can be distinguished from the main form by its smaller size, wide-based leaves and larger capitula. Its involucral bracts are narrower and longer and their long hairs are usually very dark, but both the hairiness and the colour change a lot. Knowledge of the way that narrowleaf hawksbeard mutates is very incomplete and e.g. there is a stand that is growing in Kymenlaakso on the Gulf of Finland that differs from the main form and is nowadays regarded as approaching the original form of ssp. nigrescens. True narrowleaf hawksbeard ssp. nigrescens only grows in two places in Finland, in Utsjoki and Salla, on rocky shelves against vertical faces. Narroeleaf hawkbeard can easily be mistaken for a member of genus Hieracium, which are difficult to identify, but narrowleaf hawksbeard’s capitula are surrounded by involucral bracts which overlap in many rows.