From North America to the Holy Land

October 12, 2021




Photographer: Menashe Davidson

Summary Author: Menashe Davidson‏ 

Heterotheca subaxillaris (camphor weed), a North American plant, is an important invasive species in the Middle East. This plant was introduced in Israel in 1975 to stabilize the coastal sand dunes in Israel. It quickly occupied areas that hadn’t yet been exploited by native species. A rapid evolutionary change occurred within the introduced populations, favoring root resources allocation, that allowed this species to establish and expand its range, thus successfully invading the ecosystems of coastal areas and eventually the soils of cultivated lands.

The above photos were taken in my citrus plantation, in Tira, Israel, on May 2021. They demonstrate the evolutionary changes that enable this species to access any moisture in the ground, gain nutrients from the soil and flower under the hot, summer sunlight.

Picture 1- Citrus plantation plot. Notice that it’s free of weeds

Picture 2 – Adjacent plot. Here, the citrus trees were uprooted one year ago. This plot is now infested with Heterotheca.

Picture 3 – The camphor weed reproduces only by seeds. Hairs on the small seeds assist wind dispersal.

Picture 4 – Seedlings of Heterotheca germinate in the wet soil of drip irrigation, along the margins of the citrus plot. A basal rosette of leaves grows from which a tall shoot emerges carrying a number of flowers.

Bottom photo: Invasive plant in 1-year old citrus plantation.


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