Utricularia

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Utricularia

Description

Annual or perennial aquatic terrestrial or epiphytic herbs always of damp places, without true roots or leaves but with stems modified in various ways to function as rhizoids, stolons and foliar organs, all species bearing small complex bladder-like traps for the capture and digestion of small aquatic organisms. Inflorescence racemose, peduncled, usually simple, bracteate; Stamens 2 inserted at the base of the upper lip; Ovary globose or ovoid, ovules 2-many on a free basal or free central ± fleshy placenta; Capsule globose or ovoid, dehiscing very variously by longitudinal slits, dorsiventral or rarely lateral valves, pores or circumscissile or rarely indehiscent. Seeds 1-many, very variously shaped and sculptured.

Distribution

Africa: present America: present Asia: present present Asia-Temperate:, China South-Central (Yunnan present) Asia-Tropical:, Borneo present; India absent; Malaya presentpresent; New Guinea presentendemic; Philippines (Philippines present); Thailand (Thailand presentpresent) Australasia: Burma: present Cosmopolitan but mostly in the tropical zone: present N. Australia: present New World: present North Sumatra: present Old World north temperate zone: present SE. Australia: present SE. New Guinea: present SW. China: present Tropical Africa: present present present present present northern Australia: present tropical America: present tropical Asia: present
Cosmopolitan but mostly in the tropical zone. About 180 spp., almost half of which occur in the New World, the rest more or less equally distributed between tropical Africa, Asia and Australia with a few in the north temperate zone; in Malesia 22 spp.
The geographical relationships of the Malesian spp. are of some interest. Twelve species are more or less widespread throughout tropical Asia and Australia and four of these occur also in tropical Africa. U. subulata is widespread in tropical America and Africa, apparently absent from India, but present in Thailand, Malaya and Borneo. U. pulchra, which is allied to the very widespread U. striatula, appears to be endemic in New Guinea while U. salmnensis of the same affinity is known only from the Gajo mountains of North Sumatra and from SW. China (Yunnan). U. vitellina is apparently local-endemic in Malaya while the allied U. involvens is known from that country, adjacent Burma, Thailand, and N. Australia. U. heterosepala, a slightly anomalous species in the same group (which is predominantly Asian but with representatives in tropical Africa and to a lesser extent in America) appears to be endemic in the Philippines. The circumboreal species U. minor occurs at high altitudes in New Guinea and U. australis, which is widely distributed in the Old World north temperate zone, occurs, mostly at high altitudes, in a number of places in Malesia; it is known also in the mountains of tropical Africa and at lower altitudes in SE. Australia. Two species known otherwise only from northern Australia occur in SE. New Guinea: U. chrysantha and U. muelleri. One strange apparent absence from the Malesian region is U. stellaris which is known from tropical Africa and Asia as far as Indo-China and reappears in northern Australia. It is included in the key to the species as it seems very probable that it does occur in the area.

Pollination

The flowers often secrete nectar and in some species are fragrant. Pollination by Diptera and Hymenoptera has been observed and the flowers are sometimes visited by Lepidoptera. However, self pollination is probably usual and cleistogamous forms are frequent and in some species inflorescences normally bear both cleistogamous and chasmogamous flowers.

Dispersal

Dispersal over short distances can easily take place in aquatic species by floating of entire plants or parts thereof, or by dispersal of buds (turions), according to RIDLEY ().

Seeds are mostly very small and sometimes winged and therefore perhaps sometimes dispersed by wind, although gravity is probably the most normal agent. In some of the aquatic species the seeds do not float, or they do so only for a time (). A few (not Mal. spp.) growing in swiftly flowing water have seeds with a mucilaginous testa and in the epiphytic species the seeds are either very small (orchid-like) or winged or (U. striatula) beset with glochidiate processes. .

The occurrence of some species which are epiphytic among moss on tree-trunks in dense primary rainforest where there is hardly any wind might point to very short-distance dispersal by ants or other insects. .

In open terrain the seed qualities would point to wider exozoic dispersal by migrating waterfowl and waders for aquatic species, and by wind. This might induce dispersal enthusiasts to explain the enormous disjunct gaps in the range of U. minor between Burma and New Guinea, and that of U. stellaris between Indo-China and Australia by erratic long-distance dispersal.

However, several terrestrial species show similar wide disjunctions, e.g. U. salwinensis between Yunnan and North Sumatra, U. scandens and U. limosa between the Malay Peninsula and New Guinea, and U. baouleensis between Luzon and Java. Though the present revision is based upon some 2000 collections, the latter two species may have escaped attention of collectors in intermediate stations. However, the disjunct range of the subalpine U. salwinensis is certainly a real gap, as high mountains are at present absent between Yunnan and N. Sumatra. A similar disjunction is found in the ranges of other high mountain plants, such as for example Swertia bimaculata and Viola biflora which are certainly not overlooked.

It should be admitted, though, that Utricularia must often have escaped attention of collectors, especially in seasonal areas where flowering is of short duration and ephemeral. On the other hand in a thoroughly explored island as Java, U. baouleensis is known only from Madura I. in one collection. This leads to the conclusion that it is most unlikely that the gaps mentioned above will be reasonably filled by later exploration, especially these of the high altitude species. This argument is strengthened by the fact that these disjunctions are by no means unique: the gap of U. salwinensis is matched by that of Viola biflora, Hedyotis verticillaris, etc., the gap of U. minor by that of Dr oser a rotundifolia and several Carices, but also by that found in Fagoideae. Even an extraordinary range as that of U. livida, which is found in East Africa and Madagascar but also in Mexico, is ± matched by a few other taxa or affinities with similar disjunction, in tropical America, e.g. tribe Ravenalae (Musaceae) and Rheedia (Guttiferae).

Then there are some Indo-Australian species showing a huge disjunction: U. involvens, Burma, Thailand, Malaya and N. Australia, and a closely related one, U. odorata, Thailand, Indo-China and N. Australia.

It gives thought to the assumption that these disjunctions cannot simply be explained by erratic longdistance dispersal. Also the occurrence of three local-endemic species makes such a correlation with dispersal capacity highly dubious and does not plead for easy dispersal. Neither does the fact that the ecology of many Utricularia spp. is very wide; they are not particular to soil, many are found in the tropics under both everwet and seasonal climatic conditions, and a fair number have a very large altitudinal range.

On the other hand it must be realized that the very widely distributed U. australis, which ranges all over the Old World with isolated sporadic localities on the southern hemisphere, is not known to produce fruit and seed, which forces to assume dispersal of small particles of its vegetative parts by migrating birds. This implies that such parts should be capable to withstand desiccation which will certainly happen during such migratory flight. Experiments could add some evidence. It is e.g. shown by V. A. WAGER () that U. australis (under the erroneous name U. stellaris) forms resting buds towards the end of the season which may carry the plant over until the following spring. These resting buds are not damaged by exposure to drought; buds taken from a herbarium specimen six months old put into an aquarium slowly swelled and developed into healthy plants.

Morphology

The most remarkable feature of the genus are the traps. They are minute vesicles provided with an apical orifice at the ventral side. The narrow opening leading to the water-filled cavity is formed by a ventral lip, and a dorsal valve which enables the prey to enter, but prevents it from escaping, in which it is also hampered by glandular papillae of striking structure. The inner wall of the trap is densely glandular-papillose and exudes proteolytic enzymes.

The functioning of the trap, by the opening of the valve, is caused by irritation of the sensitive hairs on this lid by which small Crustacea or other matter is 'sucked' in. See E. MERL () extracted by , and especially ; furthermore the excellent survey by Y. HESLOP-HARRISON ().

Cytology

Relatively few (about 15%) of the species of Utricularia have been examined; the chromosomes are apparently small and not easily observed. Basic numbers of x = 7 and 9 seem to predominate but x = 6, 8, 10, 11 and 15 are recorded. An American species, U. inflata WALT., has 2n = 18 and 36, the latter being morphologically gigantic whereas the closely allied U. radiata SMALL has 2n = 28. The common Australian species U. dichotoma LABILL. has 2n = 28 while conversely a morphologically small variant of this, U. uniflora R.BR., has 2n = 56. Cf. .

Notes

The study of Utricularia has always been hampered by badly collected and inadequate material. Of the aquatic species the vegetative parts should be suitably supported by a (rigid) sheet of paper and thus be raised out of the water in their natural position and then dried as rapidly as possible. Additional inflorescences and infructescences should be added. Terrestrial species have often not very obvious vegetative parts which are usually beneath or in the substrate. They must be carefully 'unearthed', or dried with the adhering mud.
Specimens in liquid are of course excellent. FAA is not so suitable; the best solution is a mixture of 50-55% alcohol, 40% water and 5-10% glycerine; the latter may be omitted or even added later; it is important that the receptacle is entirely filled with liquid.
It is important to take many flowers but see that also fruit and seed are represented.
As two or more terrestrial species are frequently growing together, with their vegetative parts intimately mixed in the substrate, care is needed in collecting. It is important to note the flower colour; this is in several species very variable.
Hardly any Utricularia spp. have been collected in the Lesser Sunda Islands. Though this archipelago is subject to a dry season, collecting at the the end of the wet season in rice-fields, shallow swamps and damp grassland may yield interesting results, as several species have been found in the adjacent Madura & Kangean Islands which have the same climatic regime.

Citation

BENJ. - in Linnaea. 1847: 447
A.DC. - in DC., Prod. 8. 1844: 3
KAMIENSKI - in E. & P., Nat. Pfl. Fam. 4. 1895: 122
P. TAYLOR - in Kew Bull. 1964: 1
PELLEGR. - in Bull. Soc. Bot. Fr. 1914: 514
BARNH. - in Mem. N.Y. Bot. Gard. 1915: 58
LINNE, Sp. Pl. 1753: 18
KAMIENSKI - in Bot. Jahrb. 1902: 113
PERRIER - in Mém. Inst. Sci. Madag. 1955: 199
PELLEGR. - in Bull. Soc. Bot. Fr. 1914: 20
BENJ. - in Humbert, FL Madag., Lentib. 1955: 19
B. & H. - in Gen. Pl. 1876: 987
LINNE - in Mem. N.Y. Bot. Gard. 1967: 206
MELCHIOR - in Engl., Syll. Pfl., ed. 12, 2. 1964: 467
KOMIYA - in J. Jap. Bot. 1973: 149
KAMIENSKI - in E. & P., Nat. Pfl. Fam. 4. 1895: 119
GRISEB., Cat. Pl. Cub. 1866: 162