Identification notes
This hornwort is more likely to be found in cultivated ground (especially stubble fields on heavy, circumneutral soils) than the similar-looking A. punctatus. It is a pioneering species with a short life-cycle and the female ‘horns’ are often present. As in A. punctatus, it is the male structures that are most important in identification, and the dimensions of the antheridia will need to be checked to confirm the species. They can easily be squeezed out of the wart-like antheridial cavities on the upper surface of the thallus with fine-tipped forceps.
If horns are absent, you can be certain you have a hornwort by looking for the scattered tell-tale dark dots of Nostoc cyanobacterial colonies in the thallus (hold it up to the light to see these). In Blasia, the only thallose liverwort which also has a symbiotic association with Nostoc, the colonies are restricted to a single line on either side of the thallus. Each hornwort thallus cell also has a single, very large and plate-like chloroplast, another useful point of difference from thallose liverworts.
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