Spear-leaved orache
Other names
Hastate orache, halberd-leaved orache
Latin names
Atriplex prostrata Boucher ex DC (Atriplex hastate L.)
Weed Type
Annual Broad-leaved Weeds
Occurrence
Spear-leaved orache is a summer annual with a prostrate habit that occurs on most soils. It is found on waste and cultivated land throughout Britain. Spear-leaved orache is a halophyte and can tolerate some salinity and alkalinity. It can survive on the sides of road where salt has been applied overwinter. It is normally associated with soils rich in nitrogen but is known to readily colonise fly ash, the fuel waste from power stations.
In a preliminary survey of UK weeds in 1971-1973, it was common in 4% of the areas surveyed.
Plants are very variable in morphology. Spear-leaved orache is rich in vitamin C and has been used as a vegetable. The plant is digestible by ruminants. In Canada it has been grazed heavily by sheep, however, it may be mildly poisonous if large amounts are fed to the exclusion of other forage.
Biology
Spear-leaved orache flowers from July to September. The flowers are primarily wind pollinated but are also visited by insects. The seeds mature from August to October. The average seed number per plant is 13,760. The seeds are of 2 types. The larger seeds are reddish-brown and flattened, the smaller and more numerous ones are rounded, black and glossy.
In germination tests the brown seeds gave 100% germination within 6 months. The black seeds gave less that 10% germination over the same period. Scarification of the hard coat of the black seed promoted rapid germination. Dormancy is broken by chilling. Seeds germinate best in alternating temperatures but do not respond to light. In the field, most seedlings emerge from March to May with a peak in April.
Spear-leaved orache is a C3 plant in terms of carbon fixation during photosynthesis.
Persistence and Spread
The two types of seed exhibit marked differences in soil longevity. The brown seed shows little delay in germination while the black seed germinates sporadically. Being more dormant, the black seed are able to survive in soil for more than 5 years.
There is no obvious seed dispersal mechanism.
Management
Control is by surface cultivations in spring, hoeing of root crops and hand pulling of larger plants to prevent seeding. The introduction of the weed through contaminated crop seed should also be avoided.
Updated October 2007.