A recent study by Mattingly and colleagues, published in AoB PLANTS, offers new insights into how the horticultural plant Lythrum virgatum, European wand loosestrife, could impact the invasive plant Lythrum salicaria, purple loosestrife. The research indicates that Lythrum virgatum might introduce meaningful trait variation by escaping into established Lythrum salicaria populations or by hybridising with Lythrum salicaria. These findings suggest that Lythrum virgatum could potentially assist rapid evolution and local adaptation in Lythrum salicaria.
Lythrum salicaria is a Eurasian perennial and a North American headache. Mattingly and colleagues report that damage and management of Lythrum salicaria cost up to $80 million each year. One of the reasons it’s a problem is that the plant is adaptable and has been able to spread across latitudes to invade new territories. This flexibility has led to a lot of study of its genotypes. Biologists had thought it was getting some help from cross-breeding with native Lythrum species, though there’s no firm evidence of this. But now another Lythrum species might be a problem.
Lythrum virgatum is often sold as a sterile and non-invasive alternative to Lythrum salicaria, but that’s inaccurate. Mattingly and colleagues say that Lythrum virgatum cultivars are self-sterile, but if there are other Lythrum virgatum plants, they can produce many seeds. Lythrum virgatum can easily cross-breed with Lythrum salicaria, so much so there’s debate over whether they are actually two different species. Mattingly and colleagues write in their article that there are commercial reasons to divide the two species.
Horticulturists benefit from taxonomic splitting because L. virgatum is less often regulated than L. salicaria (though an increasing number of governments are doing so). Conservationists would benefit from considering them the same species, because any regulations applying to L. salicaria would then also apply to L. virgatum.Mattingly et al. 2023
Mattingly and colleagues researched the potential for problems from Lythrum virgatum and Lythrum salicaria invasion and hybridisation by conducting a greenhouse common garden experiment, comparing the traits and flood response of Lythrum salicaria and Lythrum virgatum collected from two sources each in their native range. The researchers hypothesised that the two wetland taxa would have comparable responses to flooding and that flood tolerance would correlate with higher fitness.
The study’s results showed that Lythrum virgatum exhibited stronger stress responses to flooding than Lythrum salicaria. Lythrum virgatum shifted more aboveground allocation away from reproduction, decreased inflorescence biomass by 40% more, and produced 7% more stem aerenchymatous phellum, a specialised tissue that maintains aeration. Despite these more pronounced responses to flooding stress, Lythrum virgatum demonstrated higher fitness (inflorescence biomass and reproductive allocation) than Lythrum salicaria.
Lythrum virgatum persisted under flooded conditions and produced more reproductive biomass than Lythrum salicaria, both in flooded and non-flooded conditions. However, inundation stressed Lythrum virgatum more than Lythrum salicaria. The research suggests that Lythrum virgatum may be able to establish itself in the wetland habitats where Lythrum salicaria thrives but could potentially possess broader habitat tolerances. Mattingly and colleagues offer some hope of natural defences against such an invasion.
Other environmental factors surely control establishment and persistence of L. virgatum in nature. For example, specialist beetles incur greater damage on early-flowering genotypes (Lehndal and Ågren 2015) and might prefer L. virgatum, especially because it is less hairy.Mattingly et al. 2023
However, hybridisation means that Lythrum virgatum could give useful traits to Lythrum salicaria.
Studies indicate that hybridization is not only possible (Anderson and Ascher 1993; Lindgren and Clay 1993; Ottenbreit and Staniforth 1994; Amon et al. 2007) but likely, meaning the unique trait variation we have documented for L. virgatum could introduce adaptive novelty into long-established L. salicaria invasions.Mattingly et al. 2023
This discovery could have significant implications for the study and management of invasive plant species. If Lythrum virgatum can introduce trait diversity into Lythrum salicaria populations, it may contribute to rapid evolution and adaptation, potentially exacerbating the invasive plant’s impact on local ecosystems.
READ THE ARTICLE
Mattingly, K.Z., Braasch, B.N. and Hovick, S.M. (2023) “Greater flowering and response to flooding in Lythrum virgatum than L. salicaria (purple loosestrife),” AoB PLANTS, 15(2), p. lad009. Available at: https://doi.org/10.1093/aobpla/plad009.