Oxalis pes-caprae

Below ground O. pes-caprae is a complex plant. An underground rhizomatous stem, joins the leaf crown to the deep seated parent bulb. Below the parent bulb the stem tapers to a fine thread then swells into a fleshy tuber. Initially acting as a food storage organ, in late spring the tuber shrinks as it loses moisture, contracting and pulling the new bulbs deeper into the ground. During the growing season it is common for two bulbs to develop inside the old bulb and one on the tuber. Many bulbils, often more than 20, develop on the rhizomatous stem above the bulb.

O. pes-caprae is predominantly spread through dispersal of the numerous bulbils. During vegetative growth, cut sections of the stem are also capable of forming new plants. Without disturbance, infestations spread by sending out the underground stem at an angle, thereby allowing the contractile tuber to pull the new bulbils sideways.

Oxalis purpurea

The large bulb of O. purpurea is found close to the soil surface, 2 - 5cm deep. After flower development, bulbils form just below the soil surface on the rhizomatous stem. Horizontal rhizomes can also develop roots and shoots, forming new plants. O. purpurea is not known to set fruit in Australia.

O. purpurea also spreads by dispersal of bulbils, supplemented by the production of new plants from horizontal rhizomes.

Click to enlarge	Oxalis purpurea. New bulbs forming along the stem, above the old four o'clock bulb. In this species the new bulbs are often tightly clustered just below the soil surface

 

Oxalis glabra

The small bulbs of O. glabra are located 5-10cm below the ground (Fig 3.). Towards the end of flowering, bulbils are formed along underground stolons (horizontal stems) which spread out from the stem just above the parent bulb. At flowering, the parent bulb is exhausted and can be squashed between your fingers without resistance.

O. glabra appears to spread by fine underground stolons, a bulbil forming at the tips and developing into a new plant.

Click to enlarge

Oxalis glabra. A stolon of fingerleaf oxalis arising from the base of the leaf crown, grows horizontally just below the soil surface before forming a new bulb some 8cm away.

 

Bulbs and/or bulbils of all three weeds are:

• Easily introduced to bushland in contaminated soils and garden refuse, or on earthmoving machinery and tools.
• Rapidly spread by soil disturbance or cultivation.
• Carried by water - both bulbs and bulbils float.
• Spread by birds - Oxalis patches have been recorded under roost sites.