- Name also: Tall Wormwood, Beach Wormwood, Field Southernwood, Field Sagewort, Prairie Sagewort, Field Sagebrush
- Family: Daisy Family – Compositae, subfamily Asteroideae
(formerly Aster Family – Asteraceae)
- Growing form: Perennial herb. Rootstock strong.
- Height: 20–80 cm (8–32 in.). Many-branched. Stem often ascending, base woody, tough, virtually glabrous, usually dark reddish brown. Lacking fragrance.
- Flower: Single flower-like 2–3 mm (0.08–0.12 in.) (ssp. campestris) or 3–5 mm (0.12–0.2 in.) (ssp. bottnica) capitula surrounded by involucral bracts. Capitula flowers yellowish brown–reddish, tubular, small. Stamens 5. Pistil of 2 fused carpels. Involucre hemispherical, involucral bracts in several rows, with broadly membranous margins. Capitula broad (ssp. campestris) or compact (ssp. bottnica) in a racemose cluster.
- Leaves: Alternate, lower stalked, upper stalkless, stipulate. Blade slightly fleshy, hairy when young, later becoming glabrous (ssp. campestris) or sometimes hairy (ssp. bottnica), 2–3 times pinnately lobed, lobes thread-like, narrow, sharp-pointed.
- Fruit: Long, light brown, approx. 1 mm (0.04 in.) long achene.
- Habitat: Meadows, dry meadows, roadsides, railway embankments, sand pits, wasteland, sandy parts of sea shores, shingle, crevices.
- Flowering time: August–September.
- Endangerment: Ssp. bottnica is critically endangered and protected in all of Finland.
Field wormwood’s structure has features that are typical of dry-habitat plants and it grows on dry meadows, gravel beds and rocky embankments, even in cracks in the wall. Field wormwood is split into two subspecies. Ssp. campestris is apparently a native wild plant on the Åland Islands and the Turku archipelago, to where it has probably spread from across the sea – or more likely ice – from Estonia. Stands on islands in the Gulf of Finland can also be partly due to ancient mariners, and indeed the species is a guide and indicator of Iron Age settlement. It has clearly only spread along the southern coast and to harbour towns on the Gulf of Bothnia with people, and it continues to spread inland from the coast along the railway network. It can be found growing as a casual alien as far north as western Lapland.
The other subspecies, ssp. bottnica is clearly a native plant which has possibly even emerged in Finland, and is an endemic or indigenous subspecies which grows nowhere else in the world. It grows as a relic and depends on only one original stand at the top of the Gulf of Finland on the coasts of the islands around the Kemi–Tornio region. As a coastal plant ssp. bottnica is critically endangered and is protected, but it has managed to spread along northern railway embankments and can nowadays be found growing beside the Kolari line to the north and the north-eastern Rovaniemi–Kemijärvi, and to the south it has reached Ylivieska and around Vaala on the Kainuu line. The subspecies cross-breed at least sometimes in man-made places and the railway stands are possibly influenced by ssp. campestris. It is not always easy to differentiate between the subspecies. The hairiness and appearance of the plant generally varies quite a lot but ssp. bottnica is usually silk-haired even when it is old, and the capitula are quite large compared to ssp. campestris. Field wormwood looks a lot like mugwort (A. vulgaris), but the lobes on the leaf blades are very long and narrow and the plant looks more delicate in general.