- Name also: Wood Groundsel, Woodland Ragwort, Mountain Groundsel
- Family: Daisy Family – Compositae, subfamily Asteroideae
(formerly Aster Family – Asteraceae)
- Growing form: Annual herb.
- Height: 20–50 cm (8–20 in.). Stem branchless–branching from top, grooved, usually with straight or glandular hairs. With strong fragrance.
- Flower: Single flower-like approx. 5 mm (0.2 in.) capitula surrounded by involucral bracts. Capitula flowers yellow, ray-florets tongue-like, often curled up, sometimes lacking; disc florets tubular, small. Stamens 5. Pistil of 2 fused carpels. Involucre narrowly cylindrical–conical, often slightly alternate, involucral bracts in 1 row, very narrow, short-haired, light green, often with black tips; outer bracts at base of involucre 2–5, small, very narrow, usually with slightly dark tips. Capitula 1 or many borne in a corymbose cluster.
- Leaves: Alternate, lower short-stalked, upper stalkless, amplexicaul. Blade narrowly obovate–lanceolate, usually lobed, thin, at least underside short-haired, lobes sparsely toothed–with entire margins.
- Fruit: Cylindrical, ridged, sparsely haired, dark brown, approx. 2.5 mm (1 in.) long achene, tip with unbranched hairs.
- Habitat: Rocky outcrops, logged and burned areas, fields, meadows, roadsides, embankments, sand pits, wasteland.
- Flowering time: July–September.
As a rule, annual genus Senecio plants that grow in Finland shun competition with other plants and are mainly found in open places. Their cypselas are especially light, giving them a good possibility to spread from one open habitat to another. Its cypselas have flying hairs, whose silvery white colour has probably given the genus its scientific name – the Latin word senex means ‘old man’ and has also given us the English word ‘senile’. Heath groundsel’s kingdom is the southern Finnish coastline on acid soil and forested rocky outcrops, where it can sometimes be abundant, or very sparse in a dry summer. Inland conditions are normally too dry for it to survive so it has not spread far from the shore. It is casual in the north.
Heath groundsel can be found growing near people, mainly on roadside gravel, newly-dug ditch banks and sometimes fallow cereal fields. It doesn’t really thrive on rich cultivated ground, unlike its relative common groundsel (S. vulgaris), but otherwise it is easy to confuse the two species. Heath groundsel’s capitula usually have clear ray-florets, even though they are very narrow and often curling into a roll. Common groundsel on the other hand usually has no ray-florets. There are other differences when one takes a closer look: heath groundsel is slimmer, has longer internodes and is taller, and its capitulum is narrow and erect. The base of its involucre has only 2–5 outer bracts, and their triangular tip is not blackish. Heath groundsel is pollinated by flies and hymenopterans. Sometimes the pollen gets delivered to the wrong address and heath groundsel can cross-breed with common groundsel and sticky groundsel (S. viscous) when they are growing in the same habitat.