On the other foot, being a landlubber, 1 have trouble when near the coast in identifying
some of the maritime Atriplex species and hybrids. The Willow herb genus Epilobium is
another that folks have trouble with. Epilobium tetragonum, with its narrow, waxy,
blue-green leaves that redden in exposed sites, is probably the commonest species of
arable, waste ground and allotments - but I seldom find it on lists I am sent. Most people
assuming that anything that is not Great Hairy Willow herb E. hirsutum must be the
American Willow herb, E. ciliatum (formerly E. adenocaulon) - which again, we find
to be far less common that it used to be. E. parviflorum, E. montanum and E. roseum
are also common on arable land. Although Epilobium obscurum is typically a plant of
bogs and marshes, it also occurs in pavement cracks and at the base of walls. In identifying
Epilobiums, the globular ends of the stalked glands must be looked for while fresh in the
field as they disappear as soon as plants begin to wilt. Finally, a grass that it's easy to get
wrong. The very local Orange Foxtail has orange anthers, while in its more familiar
look-alike, Marsh Foxtail they are lilac - until they have dehisced that is, - when in the
case of both species they are dull orange. To be sure one needs to check the relative
length of the awns.
Grid References
Nowadays, it is possible to attempt to locate the geographical position of a plant in the
field using a GPS locked onto orbiting American satellites. Their accuracy is seldom
better than +30m in the horizontal plain however, and if you sit on the spot for a while
you will see the numbers on your display gradually fluctuating. Let us suppose that the
'actual' reference is TL8000,2000 - this would locate you to the closest 10m square.
Since you are on the intersect of both the 8000 and the 2000 grid lines however, a
fluctuating error of 30m will result in the full reference ranging from TL7997,1997 to
TL8003,2003. Thus a +30m accuracy reference might actually put you in the wrong
10km square. Nevertheless, in wide flat open areas a GPS is usually adequate. Where it
comes unstuck, however, is in woodland, where signal reflections from trees can lead to
large errors, despite the fact that the readings are repeatable and can be used to refind a
site. Many people have trouble because they have not calibrated their's properly. There
are large numbers of national grids to choose from in the built in memory, and one lady
was having trouble because her's was set on the South African grid. If you are making a
list for a single site, or attempting to define the location of a rarity, just check on a
1:25,000 map and see if the GPS reading makes sense.
Similar problems occur using O.S. maps. Quite often botanists use 1:50,000 maps to
determine their grid references, locating themselves spatially, relative to some
recognizable feature on the ground such as a road, or building. On maps of this scale
however, the widths of roads and the sizes of buildings are often markedly exaggerated
and simplified to make them discernable, and here again it is possible to end up in the
wrong 100m square or even the wrong 10km square. On 1:25,000 maps the scaled sizes
of features are much closer to reality and one can be reasonably certain of assigning the
correct 100m square. Providing that is, you have used a measuring tool rather than
10
Essex Field Club Newsletter No. 55, January 2008