Bromus hordeaceus

Bromus hordeaceus L. (syn.: B. mollis L.) (Eur., As., N-Afr.) – A critical species with numerous infraspecific taxa, most of which only have a restricted taxonomic value. In Belgium, four subspecies are currently found: subsp. hordeaceus, subsp. thominei (Hardouin) Br.-Bl. (syn.: B. thominei Hardouin) (both native) and subsp.longipedicellatus and subsp. pseudothominei (most probably not native). Typical plants are usually readily distinguished but intermediate forms sometimes occur. Therefore, they probably do not merit specific rank. An additional subspecies was formerly recorded as an ephemeral alien: subsp. molliformis (Lloyd) Maire et Weiller.

1. Lemma 8-10(-11) mm long, usually pubescent (more rarely glabrous), with obtuse marginal angle. Awn 4-11 mm long, straight. Inflorescence up to 10(-20) cm long, more or less lax to contracted === 2

1. Lemma less than 8 mm long, usually glabrous (more rarely pubescent), margins rounded or with an obtuse angle. Awn 2-7 mm long, straight or slightly curved out. Inflorescence 1,5-10 cm long, usually contracted === 3

2. At least 4 pedicels or panicle branches longer than their spikelets. Stem often robust, up to 150 cm long === subsp. longipedicellatus

2. All or at most 3 pedicels or panicle branches longer than their spikelets. Stem shorter, up to 80 cm long (native) === subsp. hordeaceus

3. Stem less than 20 cm tall, procumbent to ascending. Inflorescence up to 4(-5) cm long (often very few-flowered). Lemma usually with rounded margins. Awn slightly curved out at maturity. Palea equaling caryopsis (native) === subsp. thominei

3. Stem 20-70(-110) cm tall, erect. Inflorescence (2,5-) 4-10 cm long (usually with numerous spikelets). Lemma usually with obtuse marginal angle. Awn straight. Palea slightly exceeding caryopsis === subsp. pseudothominei

subsp. longipedicellatus Spalton (W-Eur.?) – A very rare and probably ephemeral alien but possibly poorly known and under-recorded. In the herbarium of the National Botanic Garden a specimen is preserved from the 19th century, without further details. Recorded on a pond margin in Assenois in 1944. In 2011 also discovered on the verge of a potato field in Maldegem (Vossenholse Meersen) (White 2013) and in 2013 as a weed in a Phacelia field in Brussels. Doubtlessly overlooked elsewhere.

The origin of this taxon is unknown. It was recently described from the British Isles by Spalton (2001) and was subsequently recorded in Austria (Scholz & Hohla 2008), Belgium (Verloove 2006), France (Rich 2003, Portal 2004), Germany (Scholz 2008) and Switserland (Lambelet-Haüter & al. 2006). It may well be an introgressive hybrid of Bromus commutatus and B. hordeaceus (Scholz 2008). It seems to be confined to man-made habitats (often recently sown plots) and is therefore accepted here as non-native.

Up to present, the oldest known record of subsp. longipedicellatus was from Torbay (Devon) in 1926. To our current knowledge the Belgian record from the 19th century appears to be the first record ever for this taxon.

Herbarium specimen of subsp. longipedicellatus

Herbarium specimen of subsp. pseudothominei

 


Selected literature:

Lambelet-Haüter C., Schneider C. & Mayor R. (2006) Inventaire des plantes vasculaires du canton de Genève avec Liste Rouge Conservatoire et Jardin Botaniques Genève: 1-135.

Portal R. (2004) Quelques Bromus sur la sellette. Bull. Assoc. Bot. Digitalis 3: 18-30.

Rich T. C. G. (2003) Présence en France de Bromus hordaceus L. subsp. longipedicellatus L. M. Spalton. Bull. Soc. Bot. Centre-Ouest N.S. 34: 167-168.

Scholz H. (2008) Die Gattung Bromus (Poaceae) in Mitteleuropa. Synopse und tabellarischer Bestimmungsschlüssel.Kochia 3: 1-18.

Scholz H. & Hohla M. (2008) Drei für Österreich neue Taxa der anökophytischen Gattung Bromus (Poaceae). Linzer biol. Beitr. 40/1: 279-286.

Spalton L.M. (2001) A new subspecies of Bromus hordeaceus L. (Poaceae). Watsonia 23: 525-531.

Verloove F. (2006) Catalogue of neophytes in Belgium. (1800-2005). Scripta Botanica Belgica 39. Nationale Plantentuin, Meise: 89 p.

White W. (2013) Een derde waarneming van Bromus hordeaceus subsp. Longipedicellatus in België. Dumortiera 102: 45-48. [available online at: http://www.br.fgov.be/DUMORTIERA/DUM_102/Dum_102_45-48_Bromus%20hordeace...