Jim’s photograph perfectly illustrates the English common name for this species of temperate forests in the northern hemisphere: angel wings. In the written accompaniment to his photograph on Flickr, Jim also explains the scientific name: “pleur meaning ‘on the side’ a reference to the stalk being on the side of the cap, cybella meaning ‘small cap’ and porrigens meaning ‘sticking out'”.
Pleurocybella porrigens is a wood-decay fungus associated with conifers (particularly Tsuga, the hemlocks), and more specifically, a white-rot fungus (in general, these digest lignin in wood and leave cellulose behind, though they can also digest both — but lignin is less abundant, so it can give the appearance of leaving cellulose behind).
Important for some BPotD readers whenever a fungus is featured is the question of whether it is edible or not. For many years, the answer would have been “yes, but not particularly tasty”. However, see: Savuc, P and Danel, V. 2006. New Syndromes in Mushroom Poisoning. Toxicological Reviews. 25(3):199-209. In this paper, the authors describe that in Japan a “convulsive encephalopathy outbreak was reported in patients with history of chronic renal failure” after ingestion of Pleurocybella porrigens (in Japan: sugihiratake). The question as to what caused the outbreak seems to have been answered: see Wakimoto, T et al. 2011. Proof of the Existence of an Unstable Amino Acid: Pleurocybellaziridine in Pleurocybella porrigens. Angewandte Chemie International Edition. 50(5) 1168. However, the why of the outbreak of poisonings remains unknown. Michael W. Beug explores that question in Pleurocybella porrigens toxin unmasked?, an article in McIlvainea: Journal of American Amateur Mycology.