Bromus L.
(incl. Anisantha K. Koch, Bromopsis (Dum.) Fourr. and Ceratochloa DC. et Beauv.)
The generic limits of the genus Bromus have been controversial for quite a long time. Many authors have accepted the sections of Bromus at generic level (see for instance Tsvelev 1984, Ryves & al. 1996, Spalton 2004, van der Meijden 2005, Stace 2010, etc.). However, in the present account we follow Soreng & al. (2003), Pavlick & Anderton (2007) and Mabberley (2008). This also seems to be in accordance with recent molecular phylogenetic studies (Saarela & al. 2007). As here circumscribed, Bromus is a large genus of ca. 150 species (possibly up to 400 according to Pavlick & Anderton 2007, but this is rather unlikely, even when treated in a very broad sense). Most species are confined to temperate and cool regions of the world. In Belgium, 11 species (and several additional infraspecific taxa) are presumably native (or archaeophytic) (Lambinon & al. 2004): Bromus arvensis L., B. bromoideus (Lej.) Crépin (endemic in a small area in the Ardennes but now extinct), B. commutatus Schrad., B. erectus Huds. (syn.: Bromopsis erecta (Huds.) Fourr.), B. grossus Desf. ex DC., B. hordeaceus L., B. racemosus L., B. ramosus Huds. (syn.: Bromopsis ramosa (Huds.) Holub), B. secalinus L., B. sterilis L. (syn.: Anisantha sterilis (L.) Nevski) and B. tectorum L. (syn.: Anisantha tectorum (L.) Nevski).
As stated by Bor (1968) morphological characteristics are often correlated with environmental conditions (e.g. desert forms versus channel bank forms) or simply depend upon age. Likewise, pubescence of lemmas, leaf blades and/or leaf sheaths is exceedingly variable. For most species glabrous as well as pubescent forms have been described. Bor l.c., for instance, provides for most taxa of Bromus in Iraq names for glabrous and pubescent varieties.
Many identification problems are specific for one section and therefore further discussed at length under each section.
The account here presented is a preliminary one: many Belgian collections of Bromus (especially those from section Bromus) require additional study.
Key to the sections of Bromus
1. Lower glume 1(-3) nerved === 2
1. Lower glume 3-5(-9) nerved === 3
2. Plants perennial. Awns (if present) always shorter than lemma, arising less than 1,5 mm below lemma apex === Section Bromopsis
2. Plants annual. Awns always longer than lemma, arising more than 1,5 mm below lemma apex === Section Genea
3. Spikelets laterally compressed, lemma strongly keeled. Plants always biennial or perennial (sometimes short-lived) === Section Ceratochloa
3. Spikelets terete, lemma rounded on the back. Plants always annual === Section Bromus
section Bromus L.
Within the genus Bromus the taxonomy of the section Bromus surely is one of the most complex. Many diacritic features are not (always) reliable or exceedingly variable.
Lemma texture (papery with protruding veins vs. leathery with indistinct veins) is widely accepted as an important character for the separation of taxa. In practice, however, the appreciation of lemma texture is rarely obvious at first sight and requires technical preparations, namely “(…) gently prodding pre-soaked lemmas with a blunt needle (…)” (see Spalton 2001, 2004). Therefore, in the present treatment less weight is given to this character. Likewise, inflorescence shape (contracted with most panicle branches and pedicels shorter than the pedicels vs. lax with most panicle branches and pedicels longer than the branches) can vary considerably (see also Smith & Sales 1993). Hence, measurements are often contradictory in standard floras. Bromus lanceolatus, for instance, keys out as a long-pedicelled species in Flora Europaea (Smith 1980; contrary, however, to his species description: “…mostly shorter than the spikelets”!) and as a short-pedicelled one in Flora of North America (Pavlick & Anderton 2007). In fact, this feature is variable within one species (e.g. Bromus hordeaceus that has, on the one hand, a short-pedicelled subsp. divaricatus (Bonnier et Layens) Kerguélen and on the other hand a long-pedicelled subsp. longipedicellatus Spalton) and only indicative as a subsidiary feature. As mentioned before, pubescence is a worthless feature since in most species plants with glabrous as well as pubescent spikelets and/or leaves exist.
The specific boundaries between certain species doubtlessly require further investigation. Some are surely much more closely related than often presumed. A recent study (Oja & Paal 2007), for instance, revealed the very close relationship between Bromus arvensis, B. japonicus and B. squarrosus.
Awn-insertion of the lemma (distance insertion to lemma apex) is an important character within section Bromus. It should be noted however that several lemmas should be checked since this feature can vary within one spikelet.
Genuine residence status of many supposedly native taxa is critical. At least some might in fact be non-native (archaeophytes or neophytes) (see also Smith 1986). Others are perhaps (almost) extinct or have become very rare as native species but are, in turn, regularly introduced (for instance Bromus arvensis, B. secalinus).
1. At least the upper lemmas with 3 or more awns === 2
1. All lemmas with a single awn === 3
2. Lemmas without lateral auricles === Bromus danthoniae
2. Lemma with lateral auricles (native) === B. bromoideus
3. Anthers more than 3 mm long, half as long as the palea (native) === B. arvensis
3. Anthers less than 3 mm long, much shorter compared with the palea === 4
4. Caryopsis thick with inrolled margins. Lemma with margins very tightly wrapped around caryopsis at maturity (native) === B. grossus and B. secalinus
4. Caryopsis thin, flat or with feebly inrolled margins. Lemma margins not or only slightly wrapped around caryopsis at maturity (native) === 5
5. Awns strongly curving out at maturity, their apices widely diverging === 6
5. Awns straight (or nearly so) at maturity === 13
6. Inflorescence compact at maturity, all pedicels shorter than their spikelets === 7
6. Inflorescence compact to lax at maturity, at maturity at least some pedicels longer than the spikelets === 10
7. Spikelets 25-45 mm long. Awn arising ca. 4 mm below apex of lemma === 8
7. Spikelets up to 20 mm long. Awn arising at most 2,5 mm below apex of lemma === 9
8. Spikelets (sub-) sessile. Lemma narrowly lanceolate, without obvious angle, ca. 4 mm wide. Upper glume usually with a distinct awn === B. alopecuros
8. Spikelets (at least the lowermost) pedicelled, pedicel ca. 5-10 mm long. Lemma wider, with distinctly angled margins, ca. 6 mm wide. Upper glume muticuous === B. lanceolatus p.p.
9. Awn arising 1,5-2,5 mm below apex of lemma. Lemma up to 2 mm wide === B. scoparius
9. Awn arising at most 1,5 mm below apex of lemma. Lemma 3-5 mm wide === B. hordeaceus p.p. (native subspecies)
10. Lemma papery, with prominent veins when dry === B. intermedius
10. Lemma leathery, smooth when dry === 11
11. Inflorescence usually a raceme, most branches bearing only one spikelet. Lemma 6-8 mm wide with sharply angled margin === B. squarrosus
11. Inflorescence a panicle (compact or lax). Lemma less than 6 mm wide, usually with less sharply angled margin === 12
12. Panicle lax and nodding at maturity, at least some pedicels longer than their spikelets. Lemma 8-10 mm long ===B. japonicus (subsp. japonicus)
12. Panicle compact, all or most pedicels shorter than their spikelets. Lemma 11-20 mm long === B. lanceolatus p.p.
13. Awn arising ca. 2-2,5 mm below lemma apex === B. japonicus (subsp. subsquarrosus)
13. Awn arising ca. 1-1,5 mm below lemma apex === 14
14. Ripe caryopsis exceeding palea. Lemma 4,5-6,5 mm long with hyaline, sharply angled margin. Awn inserted at the bottom of the deeply cleft lemma apex === B. lepidus
14. Ripe caryopsis shorter than or at most equaling palea. Lemma 6,5-11 mm long. Awn inserted otherwise === 15
15. Lemmas leathery, nearly always glabrous, veins obscure, not protruding. Most pedicels longer than spikelets (native) === B. commutatus and B. racemosus
15. Lemmas papery, hairy or (more rarely) glabrous, veins distinct. Pedicels shorter or longer than spikelets === B. hordeaceus p.p. (incl. subsp. longipedicellatus and pseudothominei)
Additional aliens: Bromus arenarius Labill. (syn.: B. australis R. Brown) (Aus., wool alien), B. briziformis Fisch. et C.A. Mey. (As., vector unknown) and B. pectinatus Thunb. (syn.: B. adoensis Steud., B. japonicus var. pectinatus (Thunb.) Aschers. et Graebn., B. japonicus var. velutinus (Nocca) Aschers. et Graebn., B. pectinatus var. vestitus (Schrad.) Pénzes, B. vestitus Schrad.) (Afr., As., wool alien).
section Ceratochloa (DC. et Beauv.) Griseb. (syn.: Ceratochloa DC. et Beauv.)
P.S. This section was recently revised in Belgium (Verloove 2012). Belgian populations of Bromus carinatus s.l. turned out to belong with B. sitchensis.
- Lemma 7-9 veined, concolourous, always awned, awn 4-10 mm long. Palea ¾ to as long as lemma === Bromus carinatus
- Lemma 9-13 veined, often partly purplish, usually unawned or with a short awn up to 3 mm long. Palea ½ to ¾ as long as lemma === B. catharticus
Additional aliens: Bromus brevis Nees ex Steudel (syn.: B. catharticus Vahl var. rupestris (Speg.) Planchuelo et P.M. Peterson, Ceratochloa brevis (Nees ex Steudel) B.D. Jacks.) (S-Am., wool alien), B. carinatus Hook. et Arnott var. marginatus (Nees) Barkworth et Anderton (syn.: B. marginatus Nees) (N-Am., vector unknown) and B. polyanthus Scribn. ex Shear (N-Am., vector unknown).
section Genea Dum. (syn.: Anisantha K. Koch)
Typical plants in section Genea are readily distinguished but more or less intermediate forms are often encountered. Many distinguishing features are merely quantitative, not qualitative.
An additional species, Bromus fasciculatus C. Presl (syn.: Anisantha fasciculata (C. Presl) Nevski), is more or less intermediate between B. madritensis and B. rubens and might have been overlooked. It was recently recorded in Germany, relatively close to the Belgian frontiers (Fuchs & al. 2011).
Fortune & al. (2008) investigated the molecular phylogeny of this section.
1. Lemma (excl. awn) > 18 mm === Bromus diandrus
1. Lemma (excl. awn) < 18 mm === 2
2. Panicle lax with longest branches longer than spikelets, pendent (native) === B. sterilis and B. tectorum
2. Panicle dense with all or most branches shorter than spikelets, erect === 3
3. Shortest panicle branches usually at least 6 mm. Sterile florets usually less than 3 === B. madritensis
3. Shortest panicle branches up to 6 mm long. Sterile florets usually at least 3 === B. rubens
section Bromopsis Dum. (syn.: section Pnigma Dum., Bromopsis (Dum.) Fourr.)
This section is sometimes referred to as section Pnigma but Bromopsis has priority over the former (Pavlick & Anderton 2007). Many species are poorly distinguished, especially those related to Bromus erectus and B. inermis. A closer examination might reveal the presence of additional, non-native races or species. Records of Bromus erectus outside its native, natural distribution area may be suspect and should be critically assessed. Several species of section Bromopsis are introduced on purpose for land reclamation, erosion control, etc.
1. Leaf sheaths with distinct, sharp auricles, lowermost leaf sheaths with long patent hairs. Panicle with long patent branches at maturity, often pendent (native) === Bromus ramosus s.l.
1. Leaf sheaths without distinct auricles, lowermost leaf sheaths glabrous or appressed pubescent. Panicle usually more contracted with shorter, never pendent branches at maturity === 2
2. Lemma always awned, awn 2-8 mm long. Leaves 2-6 mm wide, plicate in bud. Plant caespitose (native) === B. erectus
2. Lemma usually unawned or with a short awn up to 2 mm long (very rarely longer). Leaves 6-12 mm wide, rolled in bud. Plant rhizomatous === B. inermis
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