This section is from the book "British Wild Flowers - In Their Natural Haunts Vol5-6", by A. R. Horwood. Also available from Amazon: A British Wild Flowers In Their Natural Haunts.
Though paludal, there is no record of Bladderwort in early seed-bearing beds. The present range is Europe, N. Africa, Siberia, N. America, or the N. Temperate Zone. In Great Britain it is found in the Peninsula, Channel, Thames, Anglia, and Severn provinces; in the last in E. Gloucs, Warwick, Stafford; in Wales in Glamorgan, Radnor, Carnarvon, Flint, Anglesea; in the Trent province; in the Mersey province, except Mid Lancs; in the Humber, Tyne, and Lakes provinces, except in the Isle of Man; in the W. Lowlands, E. Lowlands, except Peebles, Selkirk, Linlithgow; in the E. Highlands, except in Stirling, S. Perth; in the W. Highlands, except in Cantire, Ebudes (S., Mid, and N.); and in E. Ross and the Northern Isles. It ascends to 1500 ft. in the Highlands. It is a native in Ireland and the Channel Islands. Probably few persons that have not made systematic botanical surveys, or visited special stations for certain plants, have had the good fortune to discover the elusive Bladderwort.
Though typical of bog and marsh formations it is also found, more seldom now than formerly, in pools and ditches, and may also occur here and there in ponds, but its chief habitat is the bog-pools on the side of moist mountains. In this way it is common to either formations.
The bladders are on short stalks. They are about one-tenth of an inch long. The green translucent utricles,1 as they are called, consist of two layers of cells, the outer large, and forming many-angled cells, with smaller rounded cells in the angles. The inside of the bladder is filled with absorbent processes in groups two long and two short.2
The lower side is straight, the upper arched, and in general form it resembles a water flea. Two sets of processes surround the entrance, two long and branched above, others straight in groups around the mouth, which has a collar within, with a flap which closes the cavity, and can be easily pushed aside by a minute aquatic insect or crustacean entering, but effectually closes it once the insect is within. The walls are contracted in the entrance, and the flap is semicircular so that it cannot be pushed aside.
1 Hence the first Latin name, and also the English name. The utricle or bladder in this plant must not be confounded with the utricle or fruit in sedges (also bladder-like in form externally).
2 See Charles Darwin, Insectivorous Plants.
This is a floating plant, with much-divided leaves as in nearly all aquatic submerged plants, the branches and segments thread-like, and attached to them are numerous egg-shaped bladders or pitcher-like bodies assisting in floating and also in obtaining insectivorous matter for food. There are no roots.
The flowers of this originally terrestrial plant are single, borne onan erect scape, the corolla yellow, large, with a conical spur, in which is the nectary, the upper lip entire, equalling the palate, and the lower lip is rolled back. When the plant has flowered the bladders fill with water and sink. The calyx is divided into two segments nearly to the base. There are only two stamens.
P'hoto. J. Ward - Bladderwort (Utricularia vulgaris, L.)
The scape may be 6 in. long. The flowers bloom in June and July. It is a perennial plant propagated by division. In autumn the plant dies down, except the terminal part, and a bud is formed.
An insect alighting on the lobes of the lower lip, visiting the flower, thrusts its proboscis beneath the upper lip to reach the honey. This is secreted in the spur in the lower lip, which is in 3 parts, the spur part fitting into the upper lip and lateral lobes, and the insect touches with its back first of all one of the lobes of the stigma which project beyond the anthers. Their papillose surfaces are at first directed downwards and stand near the upper lip. The insect then touches the anthers, which open downwards, and is dusted with their pollen. The stigma is irritable, and capable of folding upwards immediately it is touched, so that pollen from the same flower cannot be applied to the stigma, and rows of hairs on its edge brush the pollen from the insect's head as it draws back. The flower is closed and accessible only to flies.
The globular capsule opens by 2 valves, bursting irregularly, and allows the seeds to be dispersed in the water and to sink or germinate in the mud at the margin.
Bladderwort is aquatic, and more or less independent of soil, though addicted to more or less upland peaty districts as a helophyte or marsh plant.
A beetle, Phyllobrotica quadrimaculata, feeds upon it.
Utricularia, Linnaeus, is from the Latin utriculus, a little bladder, from the bladder-like pitchers or floats, and the second name (Latin) suggests that it is of common occurrence, which, however, is not the case.
It is known as Bladder-snout, Bladder-wort, Hooded Water Milfoil. The latter name was applied because of the hooded flowers and finely-divided leaves.
Essential Specific Characters: 244. Utricularia vulgaris, L. - Stem submerged, floating, leaves pinnate, with filiform segments, flowers yellow, spur half as long as the lip, conical, upper lip equal to palate, margin of lower lip reflexed.