Molinia caerulea

Molinia caerulea (L.) Moench (Eur., Afr., W-As.) – Subspecies caerulea is a locally common native species, especially in heathlands. It is confined to acidic soils. Recently, an additional, non-native taxon has been recorded. Both are distinguished as follows:

• (Very) tall plant with stem often exceeding 150 cm. Inflorescence usually longer than 30 cm. Spikelets usually at least 6,5 mm long. Lemma (3,5-)4-6 mm. Rachis of the spikelets at least partially with hairs up to 0,5 mm long === subsp. arundinacea
• Moderately tall plant, stem rather rarely exceeding 100 cm. Inflorescence usually (much) shorter than 30 cm. Spikelets always smaller. Lemma 3-4 mm. Rachis of the spikelets glabrous or (more rarely) with some scattered, very short hairs (native) === subsp. caerulea

subsp. arundinacea (Schrank) K. Richt. (syn.: subsp. litoralis (Host) Br.-Bl., subsp. altissima (Link) Domin, M. arundinacea Schrank.) (C-Eur., W-As.) – First recorded in 2006 in a heathland in Beernem (Bulskampveld): scattered clumps grew among native subsp. caerulea. In 2010 furthermore seen in similar conditions in Bree-Molenbeersel (nature reserve Groot Broek).

This subspecies is the taxon usually found in cultivation and should probably be considered as a garden escape in Belgium. The distinction between both subspecies is not always straightforward and more or less intermediate forms do occur (the latter are often referred to as subsp. caerulea var. viridiflora Lej. (Trist 1998). Therefore, subsp. arundinacea is sometimes not even separated from subsp. caerulea (see for instance Barkworth 2003). However, other important sources (for instance Euro+Med Plantbase), accept Molinia arundinacea as a distinct species.

In general subsp. arundinacea is often more confined to loamy or calcareous soils whereas subsp. caerulea usually prefers slightly acidic substrate. This does not fully hold true for the Belgian records.

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References:

Barkworth M.E. (2003) Molinia. In: Barkworth M.E. & al. (eds.), Flora of North America north of Mexico, vol. 25: 7-8. Oxford University Press, New York-Oxford.

Eberle G.M. (1995) Das Pfeifengras Molinia arundinacea Schrank - eine Problempflanze auf Pflegeflächen? Berichte der Bayerischen Botanischen Gesellschaft 65: 81-86.

Frey L. (1976) Rozmieszczenie Molinia arundinacea Schrank w Europie. Fragm. Flor. Geobot. 22(3): 275-279.

Trist P.J.O. (1986) Molinia caerulea (L.) Moench subsp. arundinacea (Schrank) H. Paul, a subspecies of purple moor-grass. Suffolk Nat. Hist. 22: 57-58.

Trist P.J.O. (1990) Molinia caerulea subsp. altissima (Link) Domin: a purple moor-grass. Suffolk Nat. Hist. 26: 85.

Trist P.J.O. (1992) Molinia caerulea (L.) Moench subsp. arundinacea (Schrank) K. Richter in Cambridgeshire (v.c.29). Nat. Cambridgeshire 34: 61-63.

Trist P.J.O. (1998) Molinia. In: Rich T.C.G. & Jermy A.C. (eds.), Plant crib: 369-370. BSBI, London.

Tutin T.G. (1975) Molinia in SW Spain. Lagascalia 5(1): 73-75.