Could be mis-identified as : Rare Lords-and-Ladies (Arum italicum) which also has a yellow spathe, but the spadix is also yellow and nearly smooth.
Some similarities to :
Asian Skunk-cabbage (Lysichiton camtschatcensis) which is shorter overall with grey-green leaves and has a broader and shorter white spathe and shorter green spadix which is virtually scentless. Both species (Asian and American) are used as ornamental plants from where they can easily escape along watercourses where they become a major problem. The specimens of American Skunk-cabbage on the stream just below the gardens of Muncaster Castle probably escaped from the garden where they might once have been grown as ornamental plants, and possibly still are, there are specimens still to be found within easy sight of the castle itself (see photos above).
Some resemblance to : Lords-and-Ladies (Arum maculata), (which has a greenish-yellow turning brownish spathe with a velvety brown spadix), Arum Lily (Zantedeschia aethiopica) (which has a white spathe and velvety yellow spadix) and Dragon Arum (Dracunculus vulgaris) (which has a frilly beetroot-coloured spathe and also smells awful) to which they are all related (although many are in differing genera).
Asian Skunk-Cabbage (Lysichiton camtschatcensis) to produce Hybrid Swamp Lantern (Lysichiton × hortensis) but that has white flowers which lack aroma and occurs in cultivation.
Uniquely identifiable characteristics
Distinguishing Feature : The foul smell, the yellow spadix with pimply green/cream spadix. Unlike most other arums, the spadix eventually out-grows the spathe and peeks out slightly above it.
No relation to : Wild Cabbage (Brassica oleracea) [a plant with similar name but belonging to a differing family].
It is a non-native and listed as a problem plant of shallow wet and marshy places and still waters because it spread un-controllably in damp areas. It spreads both by underground rhizomes and by seed, but is very slow to establish, not flowering until in the 6th year. It is frequently planted beside streams and ornamental lakes and maybe later thrown out because it has spread too much. At Muncaster Gardens in Ravenglass the seeds must have flowed downstream for 500 metres for it has escaped the grounds, naturalised near the stream channel and is about to enter the River Esk lower down if it has not already done so. It dies back in winter. The curled leaves emerge at about the same time as do the flowers; the leaves growing upright to 1m and up to 1.5m long.
It is called Skunk-cabbage because the leaves have a very strong smell when crushed which some describe as 'evil' which others might describe as foul, awful, obnoxious or possibly 'skunky'. Cultivated varieties have had much of the obnoxious smell bred out. When in flower Lysichiton species do not produce heat (as does Lords-and-Ladies - but which does not belong to this genus).
The berries are red and form on the spadix where the flowers were in summer. The flower spike looks similar to that of
Sweet Flag (Acorus calamus) but that is far taller and the spike emerges from a tight opening in the stem.
It is moderately poisonous containing raphide crystals of Oxalic Acid which are so sharp and narrow as to easily penetrate and rupture individual cells causing lysis; it is thus a mechanical poison - oxalic acid is not very soluble in water. Death is a possibility if a lot has been consumed.