Bracken: Magical . . . or Toxic Invader?
The cache, a camo-taped 35mm film canister, is hidden alongside this trail which runs west parallel to the road through dense bracken from the Cow & Calf car park @ N 53 55.002 W 1 48.034 to a Y-junction @ N 53 55.100 W 1 48.480.
From there the lower trail continues down to Cowpasture Road where it crosses Backstone Beck (near GC8VEW0 Backstone Beck Bramble Bench). The upper branch heads up to a wooden footbridge over the beck and onward trails north-west to Ilkley Tarn, south-west to White Wells or south up Backstone Beck Ghyll - to access Rocky Valley and the higher moorland.
If approaching the cache from the Hanging Stones ridge, there is a wide track descending from around N 53 55.018 W 1 48.339 to the NE which meets the cache trail @ N 53 55.061 W 1 48.174 from where you head left (NW) down to the cache location.
Bracken (Pteridium) is a genus of large, coarse ferns - and pteridophytes - vascular plants that have alternating generations, large plants that reproduce by spores rather than seeds, and small plants that produce sex cells (eggs and sperm).
Brackens are noted for their large, highly divided leaves. They are found on all continents except Antarctica and in all environments except deserts, though their typical habitat is moorland. The genus probably has the widest distribution of any fern in the world.
The word bracken is of Old Norse origin, related to Swedish bräken and Danish bregne, both meaning fern. In the past, the genus was commonly treated as having only one species, Common Bracken (Pteridium aquilinum aka Eagle Fern or Eastern Bracken Fern), but the recent trend is to subdivide it into about ten species.
Like other ferns, brackens do not have seeds or fruits, but the immature fronds, known as fiddleheads or croziers (see below) are sometimes eaten, although some may be carcinogenic.
Evolutionarily, bracken is one of the most successful ferns. Huge, widespread and ancient, it is probably the most common plant in the world. It is highly invasive, and can survive in acid soils. Like heather, it is typically found on moorland and is commonly referred to by local populations in the north of England as 'Moorland Scrub'. It is also one of the oldest ferns, with fossil records over 55 million years old.
It sends up large, triangular fronds from a wide-creeping underground rootstock (rhizomes) which may 
travel >1m underground between fronds and may form dense thickets. The hidden rhizomes form 90% of the plant. The visible part of the plant - the fronds - may grow up to 2.5m or longer with support, but typically are 0.6–2m. In cold environments, it is deciduous and, as it requires well-drained soil, is generally found growing on the hillsides.
The curled tops of young fern leaves are called croziers (or crosiers) after their resemblance to the hooked staff carried by a bishop as a symbol of pastoral office
It is a characteristic moorland plant in the UK which over the last decades has increasingly out-competed characteristic ground-cover plants such as moor grasses, cowberry, bilberry and heathers and now covers a considerable part of upland moorland.
Bracken provides a good habitat for nesting birds and cover for the movement of other birds, mammals, amphibians and reptiles.
Fritillary butterflies live in habitats dominated by bracken and can be seen flying over the tops of the plant from April to mid-August. It is also one of the food plants of caterpillars of moths, such as the garden tiger, brown silver-line, small angle-shades, orange swift, gold swift, and map-winged swift.
Once valued and gathered for use in animal bedding, tanning, and for soap and glass making, weed control and as a fertiliser (as burnt bracken ash), bracken is now seen as a pernicious, invasive and opportunistic plant, taking over from the plants traditionally associated with open moorland and reducing easy access by humans.
Bracken fiddleheads have been eaten by many cultures throughout history, either fresh, cooked, or pickled. 
It is especially common in East Asian cuisine.
However, when these young fronds are damaged by a browsing animal, bracken produces hydrogen cyanide which quickly poisons the perpetrator.
It is toxic to cattle, dogs, sheep, pigs and horses and is linked to gastrointestinal cancers in humans. It can also harbour high levels of sheep ticks, which can pass on Lyme disease.
Traditionally, people walked through smoking bracken to alleviate the symptoms of sciatica and other leg aches. The leaves were also eaten to purge the stomach and relieve problems in the spleen and intestines, including broad worms.
Myths & Legends: It was said to grant perpetual youth, and that the tiny spores gave whoever held them on Saint John's Eve (23 June) the power of invisibility, folklore which is even referred to in Shakespeare’s Henry IV . . . ' we have the receipt of fern seed: we walk invisible'. See the blog page here for more on this aspect of UK fairy lore.
Witches apparently hated bracken because the Greek letter X – a symbol of Christ – is revealed when the stem is cut. In Ireland, it was known as the fern of God because it was said that when the stem is cut at three points, each point displays a letter which together spells GOD. QI: See here for 'Bracken Lore' a 2005 illustrated paper on the numerous images which may be 'seen' in cut bracken stems!
In Scotland, it is said that the plant is an impression of the Devil’s foot; while in Venezuela and Brazil, it is used in magic rituals for cleansing the soul.
See here for more info on this increasingly widespread plant, including methods used to try and control its spread.