Centipeda minima aka Spreading Sneezeweed

Centipeda minima is a small herb in the daisy family, Asteraceae. Its common name is spreading sneeze weed. Its native range starts in the Russian Far East. It reaches into tropical Asia and the South Pacific. Records place it in Japan, India, Australia, and New Zealand. They also list several Pacific islands. Kew and PFAF call it an annual: it lives one year. Useful Tropical Plants calls it a perennial: it lives for years. Thus, sources differ on its life cycle.

The plant may stand upright or lie along the ground. Many stems can branch from its base. PFAF gives a garden height of about 0.3 feet [0.1 metres]. Its stated spread reaches about 1.6 feet [0.5 metres]. Useful Tropical Plants gives stem lengths of about 0.3–0.7 feet [0.08–0.2 metres]. Some stems reach about 1 foot [0.3 metres]. These lengths do not mean the plant grows that tall. Its flowers have both male and female organs.

In the wild, this herb grows in damp, open places. It grows in river mud and at waterhole edges. It also grows in rice fields left fallow, or unplanted. In Japan, it grows on waste ground and roadsides too. Records place it in wet sites in eastern Australia. For garden use, PFAF lists full sun or light shade. It accepts sand, loam, and clay, and prefers moist soil. It tolerates ground that is mildly acid or mildly alkaline. It accepts neutral soil too. PFAF lists cultivated beds as a garden setting.

New plants can grow from seed. PFAF says to sow in trays in mid-spring. Plant young plants outside after the last frost you expect. You can also sow straight into outdoor soil in late spring. Sources differ on whether it poses a weed risk. PFAF does not flag weed potential. Useful Tropical Plants calls it a minor crop weed. That source links its low impact to shallow roots and small size.

Both plant-use sources report no known food use. In traditional medicine, people use the herb for coughs and nasal complaints. They also use it for pain and skin swelling. Smelling crushed leaves or flower heads can make people sneeze. People have also put plant pastes on swollen areas. These past uses do not prove that treatment is safe. PFAF lists no known hazards. Yet Useful Tropical Plants reports livestock poisoning in northern Australia. That report calls for care despite the herb's past medicinal use.