A New Guide for Identifying Grasses

Hilary Wallace is an experienced field botanist and habitat surveyor based in Herefordshire, who has developed a new groundbreaking AIDGAP guide to the grass species found in the UK.

Background to the Key

This book started life as a simplified key to agricultural grasses, developed at the Agricultural Botany Department at Bangor University. It was subsequently expanded and developed by Mike Prosser in the 1970s to cover 62, principally grassland, species. Over the past 30 years the key has been used extensively for teaching students on habitat survey courses; at the Snowdonia National Park Study Centre, the Field Studies Council and courses commissioned by government agencies requiring staff to conduct habitat surveys and assessments.

These courses have covered the National Vegetation Classification (NVC), farm stewardship surveys and Habitat Condition Assessments. I found that students attending these courses often had limited experience of observing or identifying grasses, claiming they were ‘too difficult’, and were thus largely ignored, despite being essential components of most habitat survey protocols. 

Feedback from students has resulted in many of the more difficult couplets in the key being revised. New features have been added and a number of species can now be keyed out via more than one route. More recently the key has been trialled as a stand alone course to Vegetative Grass Identification at the FSC.The popularity of the key is evident by the number of requests for copies from past students and their colleagues, and the feedback from surveyors who are still using it many years after completing their course.

Why are grasses important?

Grasses form the matrix of a wide range of habitats in Britain and Ireland, from species-rich calcareous grasslands to species-poor saltmarshes and mobile sand dune systems. They also provide important cover in urban landscapes, including road verges, parklands and playing fields. In some habitats grasses play an active role in habitat creation through the production of extensive rhizome systems, for instance in stabilizing mobile sand in dune systems and mud flats. In other situations, if left unmanaged, dense tussock forming species can threaten the conservation value of species-rich habitats through unchecked growth.

Thus the nature of growth and colonisation potential of the different species can play a critical role in habitat development and conservation. The accurate classification of many habitat types, not only grasslands, using the Phase 1 habitat scheme depends on the ability to recognise a relatively small number of grass species. A greater number of species are required for a more detailed classification using the NVC. Habitat quality will also be linked to the species present and their relative abundance. Although some species are very common and have a wide tolerance to soil chemistry and moisture status, others are restricted to narrow conditions, and their presence may be of conservation importance.

Why a vegetative key?

When grasses are in flower the structure and arrangement of the floral parts into different panicle formations provides an initial guide to a species group and sometimes to the species. But keys can be complex for the beginner, since they usually require microscopic examination of the individual floral parts. In practice much habitat assessment work carried out by surveyors will involve grasses without flowers, because :

• Habitat surveys are carried out all year round
• Species have different flowering periods, even within the same habitat
• Habitat management (e.g. cutting, grazing) will affect flowering, such that flowers are often removed at the time of survey
• Unfavourable conditions (e.g. dense shade, competition from more aggressive species) will inhibit flowering

Until recently the only comprehensive key based entirely on vegetative characters was Grasses: a guide to their structure, identification, uses and distribution in the British Isles (Hubbard, 1984). Although Hubbard’s key works very well, the layout has proved daunting for beginners. More recently The vegetative key to the British flora (Poland and Clements, 2009, 2020) provides a very comprehensive key to over 200 species, including aliens, crop species, hybrids and rarities.

However, the number of species and the terminology used can be challenging to the beginner. Nevertheless Poland’s keys are invaluable to more advanced surveyors, particularly those working in disturbed or unusual habitats, and they provide additional characters that can help in difficult situations. The Identification guide to Ireland’s grasses (Fitzpatrick et al., 2016) includes a vegetative key to 75 species. There are many other local keys produced as teaching aids throughout the botanical network.

Getting started

This key is intended for use in the field and you do not need expensive or specialised equipment. The only essential things to take outside with you are a good hand lens (x10 or x20) and a ruler, for measuring leaf width etc. The Aidgap Grasses guide to identification uses a traditional dichotomous key. For ease of use the species accounts, with colour photos, concise descriptions and habitat, distribution and status information are arranged next to the diagnostic couplets, rather than as a separate section at the end. The important characters used in the key are, in order: 

• Leaf form: leaf width and leaf blade structure
• Ligule: the membranous outgrowth on the leaf blade where it joins the leaf sheath 
• Auricle: claw-like outgrowths where the leaf blade joins the leaf sheath 
• Leaf sheath: shape and hairiness
• Life cycle: annual or perennial
• Growth form: shoots dispersed or clump-forming The variety of these characteristics are illustrated by a series of diagrams and photographs.

The guide is available to order from the FSC website with an Earlybird offer of £15 if ordered by May 31st 2021: https://www.field-studies-council.org/shop/publications/grasses_aidgap/

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You can also sign up to our brand new Discovering Botany course which will equip you with the key skills needed for plant identification. https://www.field-studies-council.org/shop/courses/discovering-botany/