Bromus bromoideus

Habitat and distribution

Bromus bromoideus was endemic to a limited geographical area spanning southern Belgium and northern France. Unlike many plant species, B. bromoideus had no known natural habitat outside of agricultural settings. It was exclusively found in cultivated fields, primarily those used for growing spelt (Triticum spelta), a hulled wheat variety that was once widely cultivated in the region.

The species' natural range was confined to the Meuse district, with an extent of occurrence approximately 90 km in length and 10–15 km in width. Within this limited area, the plant showed a distinct preference for specific soil conditions, growing predominantly on poor dry calcareous soils, particularly clay-limestone or clay-schistose soils located on hills and hilltops.

Historical records indicate that B. bromoideus was commonly found in spelt fields until 1882, after which its populations began to decline. This close association with spelt cultivation is believed to have been reinforced by a synchronization between the vegetative requirements of the grass and the conditions offered by spelt agriculture. The grass was frequently observed growing in the seed line of spelt crops, suggesting it was inadvertently sown alongside the cereal.

A distinctive feature of B. bromoideus distribution pattern was its nearly exclusive association with spelt fields. With only one documented exception, the species was never observed growing in wheat or rye fields. This specificity likely relates to differences in seed characteristics between these crops; spelt has hulled grains that remain in thick glumes after threshing, producing diaspores similar in size to those of B. bromoideus, allowing the grass seeds to remain mixed with spelt during traditional harvesting and sowing processes.

At its peak distribution in the 19th century, the species was recorded in 49 locations across southeastern Belgium and one location in northern France. By the 1930s, agricultural modernization had severely reduced its range, with the last wild specimen documented in 1935.

Taxonomy

Bromus bromoideus has a complex taxonomic history with its status being subject to debate among botanists. The species shows clear genetic affinities with closely related brome grasses, particularly Bromus grossus and Bromus secalinus, leading to different interpretations of its taxonomic rank. Tournay (1968) proposed that B. bromoideus should be classified as a subspecies of B. grossus rather than a distinct species. This view was partially supported by Scholz (1970), who went further and suggested that B. bromoideus represents merely a mutant form of B. grossus. In contrast, Smith (1973) argued for maintaining its species status, emphasizing that its unique marginal lemma tooth serves as a distinctive identifying characteristic that clearly separates it from other members of the genus.

Molecular studies have provided additional insights into these relationships. Research by Ainouche and Bayer (1997) using internal transcribed spacer (ITS) sequencing revealed that B. bromoideus, B. grossus, and B. secalinus share identical ITS sequences, supporting their close evolutionary relationship. These findings align with Jauzein's (1995) assessment that B. bromoideus likely originated as a variant of B. grossus through an accidental mutation.

More recent genetic analysis using AFLP (amplified fragment length polymorphism) markers has further clarified these relationships. Koch and colleagues (2016) confirmed that B. bromoideus evolved from within the B. grossus gene pool, suggesting a relatively recent divergence. Despite this close genetic relationship, experimental hybridization work by de Cugnac demonstrated that when B. bromoideus and B. grossus were crossed, they produced B. bromoideus var. villosa (characterized by pubescent spikelets), but the defining morphological characteristics of B. bromoideus remained stable through generations of cultivation.

The most likely wild relatives of the species are considered to be B. commutatus and/or B. racemosus, which occur in less artificial habitats such as fallow land and wet meadows, respectively.

References

--

References

1. Gigot, G. (2013). [http://www.iucnredlist.org/details/165228/0 ''Bromus bromoideus'']. The IUCN Red List of Threatened Species. Version 2014.2
2. (2005-11-07). "EU project 'Ensconet' ensconces a once-lost Belgian grass". European Commission.
3. Ainouche. (1997). "On the origins of the tetraploid ''Bromus'' species (section ''Bromus'', Poaceae): insights from internal transcribed spacer sequences of nuclear ribosomal DNA". Genome.
4. (2005-10-18). "'Kiss of Life' saves extinct grass: Belgian endemic back for birthday celebrations". innovations report.
5. (2009-09-14). "Uitgestorven plant herleeft na zeventig jaar". Nu.nl.
6. (1997). "On the origins of the tetraploid ''Bromus'' species (section ''Bromus'', Poaceae): Insights from internal transcribed spacer sequences of nuclear ribosomal DNA". Genome.
7. de Cugnac, A.. (1954). "Le brome des Ardennes – l'étonnante carrière d'une espèce rare des confins ardennais". Bulletin de la Société des Naturalistes luxembourgeois.
8. (2011). "Le statut du brome épais (''Bromus grossus'') en Région Wallonne". Adoxa.
9. Godefroid, Sandrine. (2020). "A framework to identify constraints to post-extinction recovery of plant species—Application to the case of ''Bromus bromoideus''". Journal for Nature Conservation.
10. (2016). "Morphological and genetic variation of highly endangered ''Bromus'' species and the status of these Neolithic weeds in Central Europe". Plant Systematics and Evolution.
11. Maréchal, Arth.. (1937). "Note sur ''Bromus arduennensis'' Dmrt. et sur le rôle des jardins botaniques dans la conservation des espèces rares". Bulletin de la Société royale de Botanique de Belgique.
12. Scholz, H.. (1970). "Zur Systematik der Gattung ''Bromus'' L. subg. ''Bromus'' (Graminae)". Willdenowia.
13. Smith, P.M.. (1973). "Observations on some critical Bromegrasses". Watsonia.
14. Tournay, R.. (1968). "Le Brome des Ardennes, 'Bromus arduennensis' et ses proches, ''B. secalinus'' et ''B. grossus''". Bulletin du Jardin botanique national de Belgique.