Over the last two weeks I have received a few calls related to identifying a “new form of waterhemp” in Southwest Iowa. In reality, we do not have a new form of waterhemp, but a condition referred to as ‘fasciation’ (Figure 1). While this can occur in many plant species, plants like cacti and members of the sunflower family (Asteraceae) are more likely to have fasciation of stem cells. However, we’ve noticed it quite commonly on waterhemp this year, so what’s going on?
What happened with these plants is that something goes wrong with the apical meristem when trying to divide and grow. Typically cells in plant stems divide and form cylindrical or round stems for most plants. It is believed that the fasciation is caused by mutation of a single cell in the central meristem and causes cells to increase dramatically causing the growing point to develop a new plant. You could say a plant growing in another plant, so to speak. What causes plant fasciation in nature is a mystery, but environment can play a key role. Mostly this is a hormonal response to some environmental stress on the plant, but other factors could be involved. Be on the lookout for Frankenstein weeds.
Klingaman, G. 2008. Plant of the Week: Fasciated Plants (Crested Plants). University of Arkansas. https://www.uaex.edu/yard-garden/resource-library/plant-week/fasciated-2-22-08.aspx (Accessed 28 July 2020).