Overview
Oncosiphon is a genus of small annual herbs in the family Asteraceae, native to southern Africa, especially the winter-rainfall regions of South Africa and Namibia. The genus contains roughly seven species, of which globe chamomile, also called stinknet (O. piluliferum), is the species most often encountered outside Africa. Plants are upright, branched annuals 10-60 cm (4-24 in) tall, with finely dissected, almost thread-like leaves that release a strong, sharp, turpentine-like odour when bruised. The flower heads are rayless, rounded to oval yellow buttons about 6-10 mm (0.2-0.4 in) across, carried on bare stalks from late winter into spring. Each head packs many tiny disc florets that produce large numbers of small seeds. Adapted to disturbed, sandy ground, the genus germinates with cool-season rains and completes its cycle before summer drought. Several species, particularly O. piluliferum, have spread well beyond their native range and become aggressive weeds in parts of the southwestern United States and Australia, forming dense stands on roadsides and disturbed land and producing pollen and oils that can irritate skin and airways.
Native Range
Oncosiphon is native to southern Africa, mainly the winter-rainfall areas of western South Africa and Namibia, where it grows on sandy flats, disturbed ground, and roadsides.Suggested Uses
Oncosiphon has little horticultural use and is chiefly significant as a group of weedy annuals, including the invasive stinknet. In its native range it forms part of seasonal wildflower displays on disturbed and sandy ground.How to Identify
Appearance
Size & Dimensions
Height4" - 2'
Width/Spread4" - 1'
Bloom Information
Flowering runs from late winter into spring, roughly February to May in its native range and somewhat earlier where naturalised in warm climates. The yellow button heads are short-lived individually but are produced in large numbers, releasing abundant wind- and foot-borne seed as plants dry off.
Detailed Descriptions
Foliage Description
greenGrowing Conditions
Sun Requirements
• Full Sun: 6+ hours of direct sunlight
• Partial Shade: 3-6 hours of direct sunlight
• Full Shade: Less than 3 hours of direct sunlight
Water & Climate
Water Needs
Drought Tolerance
Drought tolerant when established
Care & Maintenance
Care Guide
Oncosiphon species are cool-season annuals that grow in full sun on poor, sandy, free-draining soils with a neutral to slightly alkaline pH around 6.5-8.0. They germinate with autumn or winter rain, grow quickly through cool weather, and set seed before summer heat. No feeding or irrigation is needed, and the plants spread on disturbed ground. Because several species self-seed heavily and have become invasive weeds, they are managed or removed before seed set in regions where they are not native. Crushed foliage and pollen can irritate skin and airways in sensitive people.Pruning
No pruning is practised. As short-lived annuals the plants are pulled or cut whole, and removing them before the flower heads ripen limits the spread of seed.Toxicity: Not assessed
UnknownPlanting Guide
Planting Methods & Timing
Planting Method
direct sow
