Identifying invasive cacti by the size of their seeds

C·I·B researchers Ana Novoa (C·I·B Post-doc) and Dave Richardson (C·I·B Director) together with colleagues from the University of Vigo, in Spain, identified that the seeds of cactus plants can be used as an effective way of detecting invasive cacti.

Hundreds of cactus plants are introduced to South Africa as seeds for ornamental purposes, but unfortunately many of them become serious invaders across the landscape. Although the introduction of invasive and potentially invasive cacti in South Africa should be prevented, identifying cactus species by their seeds is a difficult task for the untrained eye.

In their study, which was published in the South African Journal of Botany, the authors searched for websites selling cactus seeds and found that seeds of 266 cactus species are being traded internationally. This included 24 cactus species known to be invasive in South Africa.

The authors bought seeds of each species and found that invasive and potentially invasive species had larger and heavier seeds than non-invasive species.

Management strategies to minimize negative impacts of invasive species include the prevention of new introductions, early detection and eradication, and the control of widespread invaders. Prevention is the most cost efficient of these strategies. “Practical measures for identifying and intercepting invasive cacti before they are introduced are crucial. Seed size and mass are useful features for detecting the introduction of potentially invasive cacti,” explains Ana Novoa, “they are effective and really easy to measure”.

Difference in seed size of invasive and non-invasive cacti

The photo collage shows the difference in seed size of invasive cacti (top row) and non-invasive cacti (bottom row) (Photo collage by Ana Novoa)

Read the paper in the South African Journal of Biology

A. Novoa, J Rodríguez, A López-Nogueira, DM Richardson and L González (2016) Seed characteristics in Cactaceae: Useful diagnostic features for screening species for invasiveness? South African Journal of Botany. doi: 10.1016/j.sajb.2016.01.003

For more information, contact Ana Novoa at


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