| Oenanthe fluviatilis | |
|---|---|
 | |
Scientific classification  | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Clade: | Asterids |
| Order: | Apiales |
| Family: | Apiaceae |
| Genus: | Oenanthe |
| Species: | O. fluviatilis |
| Binomial name | |
| Oenanthe fluviatilis (Bab.) Coleman | |
Oenanthe fluviatilis, the river water-dropwort, is a flowering plant in the carrot family, Apiaceae, which is endemic to north-west Europe. It grows only in clear, unpolluted rivers and is declining throughout its range.
River water-dropwort is a hairless perennial with hollow, ridged stems up to 1 m long, submerged or floating in rivers, or emergent in marginal swamps and during periods of low flow in summer. The stems creep along the surface of mud, or on the bottom of a river, rooting at the nodes. These extend upwards through the water column, becoming thicker as they ascend, to a diameter of about an inch (2.5 cm), with a central hollow about half that size. Young plants have tubers, which disappear as they mature, leaving just fibrous roots.
The lower, underwater leaves are once to twice pinnate, with distinctive cuneate (diamond shaped) segments which are deeply divided into almost linear lobes (especially so in faster-flowing water), with petioles as long as the leaf. These submerged leaves remain green throughout the winter but the plants are much reduced, hugging the bottom of the channel. In the summer, the upper, aerial, leaves sometimes form: they are 1-3 times pinnate with ovate, lobed segments about 1 cm long, and have petioles about one third the length of the blade. The petioles on both forms are solid and produce a sheath around the stem at their base. [1]
The inflorescence is a compound umbel of 5-10 small, hemispherical umbellules, arising from the leaf nodes or from the tip of the stem. The rays do not thicken after flowering, as they do in some other species of dropwort. There are no bracts (or sometimes just one) on the main umbel, but the smaller umbellules each have 5-8 small, lanceolate bracteoles. The flowers are male or bisexual with 5 pointed sepals, 5 almost equal white petals, 5 stamens and (if present) 2 styles. The fruits are about 6 mm long with short, persistent styles less than a quarter as long as the fruit. Plants can also spread vegetatively from broken-off sections of stem, which take root readily. [1] [2]
The underwater foliage is highly distinctive, with its diamond-shaped leaves and the ability of the plant to form a carpet on the bed of the stream, which remains green throughout the winter. Flowering plants could be confused with fine-leaved water-dropwort, although that species has more highly divided leaves (4-pinnate) and larger fruits (more than 5 mm long). [2] [1]
Barring a few false starts and minor confusions, river water-dropwort was overlooked as a species until the 1840s, largely because it rarely flowers. William Higgins Coleman (c. 1816–1863) first drew attention to it when he was working on his Flora of Hertfordshire. [3] Other botanists, such as William Borrer, agreed that they had also seen it, but had assumed it was the underwater form of another species, such as cowbane.
Coleman initially reported his observations to Charles Babington who, in 1843, cautiously added it to his Manual of British Botany as Oenanthe phellandrium var. fluviatilis Bab., [4] adding that it might in fact be a full species. The following year it was elevated to species status by Coleman (with Babington's encouragement). He described it as differing from fine-leaved water-dropwort by its 'delight' in running water, the presence of stolons (stems that root at the nodes), differences in leaf shape, and its larger fruits. [5]
Because it was originally described as a variety, the type specimen refers to that (the basionym), rather than Coleman's species. A lectotype has recently been nominated by M.J.Y. Foley, of a specimen collected by Coleman from the River Lea near Hertford in 1841. [6]
There are no subspecies of river water-dropwort, but one form has been described: O. fluviatilis f. submersus, in Denmark, but it has not been widely adopted. [7] No hybrids are recorded.
Its chromosome number is 2n = 22 (based on British specimens). [1]
The generic name Oenanthe , which comes from the Ancient Greek οίνος, "wine" and άνθος, "flower", was used in ancient times for certain Mediterranean plants and later adopted to describe this genus. The epithet "fluviatilis" is derived from the Latin word for river, fluvius. [8] "Dropwort" is a reference to the tubers produced amongst the roots of certain other species in the genus, although they are not prominent in this plant. [9]
River water-dropwort is entirely confined to North-west Europe, being recorded only in Ireland, England, Germany, Austria, France, Denmark and the Low Countries. [7] In a global context it is considered to be Near Threatened (NT), with a population trend that is decreasing. It is possibly extinct in Germany. [10]
In Britain, it was first recorded by Coleman in about 1841 on the River Lea in Hertfordshire, where it still grows. [11] Earlier findings have been traced, such as a partial specimen collected by Robert Plot in the 1670s from Oxfordshire. [6] It is currently known in at least 28 English counties and it appears to have been lost from a further 14. It does not occur in Wales or Scotland, but in Ireland it is found in some 26 counties (and lost from maybe half a dozen), mostly in the centre of the island. [12]
The conservation importance of river water-dropwort is very high: it is entirely confined to clear, unpolluted river systems; it has a very restricted global distribution; and it is rare and decreasing across its range. In these regards, it is similar to highly protected species such as floating water-plantain. In Britain, it is classed as Least Concern, although it of international importance. [13] Many of its sites are classified as Sites of Special Scientific Interest, such as the rivers Avon, Itchen, Kennet and the Moors River and river water-dropwort is always considered one of the key species in the designations. [14] It is considered an axiophyte in any British county. [15]
River water-dropwort grows in clean, hard-water lowland rivers, i.e. rivers that drain geological strata with high levels of soluble calcium (chalk, limestone and various soft rocks). In the Alsace region of France, it has been found to be associated with river water-crowfoot, hornwort, fennel pondweed and perfoliate pondweed in the more eutrophic, slow-flowing reaches of that part of the Rhine, where dissolved ammonia (N/NH4) is about 45 μg/L, phosphate (P/PO4) is about 33 μg/L and calcium levels are very high (100 ppm Ca++). [16]
The River Itchen in Hampshire is typical of its habitat in Britain. In this chalk stream it grows in a community of Ranunculus penicillatus , Sparganium emersum , Schoenoplectus lacustris and Groenlandia densa , and it is associated with a wide variety of rare and protected species. [17]
Its Ellenberg values in Britain are L = 8, F = 11, R = 8, N = 6, and S = 0. [18]
There are very few references to this species in literature, presumably because it is so little-known. However, D.E. Allen [19] reports that an infusion of "water-fennel" was once used in County Wicklow as a treatment for rheumatism, although he questions whether O. fluviatilis was really the plant in question.
Oenanthe, known as water dropworts, oenanthes, water parsleys, and water celeries, are a genus of plants in the family Apiaceae. Most of the species grow in damp ground, such as in marshes or in water.
Potamogeton crispus, the crisp-leaved pondweed, curly pondweed, curly-leaf pondweed or curled pondweed, is a species of aquatic plant (hydrophyte) native to Eurasia but an introduced species and often a noxious weed in North America.
Potamogeton perfoliatus is a perennial aquatic plant in the family Potamogetonaceae occurring in both standing and flowing freshwater habitats. It is widely distributed globally, occurring in all continents except South America and Antarctica.
Potamogeton praelongus, commonly known as whitestem pondweed in North America and long-stalked pondweed in Britain, is a large, perennial aquatic plant in the family Potamogetonaceae. It is widely distributed in lakes and rivers in the northern hemisphere, but is sensitive to poor water quality.
Potamogeton polygonifolius or bog pondweed is an aquatic plant. It is found in shallow, nutrient-poor, usually acid standing or running water, bogs, fens and occasionally ditches.
Potamogeton lucens, or shining pondweed, is an aquatic perennial plant native to Eurasia and North Africa. It grows in relatively deep, still or slow-flowing, calcareous freshwater habitats.
Oenanthe pimpinelloides is a species of flowering plant in the family Apiaceae known by the common name corky-fruited water-dropwort. It is a plant of tall, lightly grazed or infrequently mown grassland and coastal meadows in Europe and neighbouring parts of Asia and North Africa.
Oenanthe javanica, commonly Java waterdropwort, water celery, water dropwort, Chinese celery, Indian pennywort, minari and Japanese parsley, is a plant of the genus Oenanthe originating from East Asia. It has a widespread native distribution in temperate Asia and tropical Asia, and is also native to Queensland, Australia.
Potamogeton alpinus is a species of perennial aquatic plant known by the common names alpine pondweed and red pondweed. It is widespread in the northern hemisphere in both rivers and lakes with good water quality.
Potamogeton gramineus is a species of aquatic plant known by the common name various-leaved pondweed, variableleaf pondweed, grass-leaved pondweed or grassy pondweed, native to the northern hemisphere where it grows in shallow, clean water.
Potamogeton nodosus is a species of aquatic plant known by the common names longleaf pondweed and Loddon pondweed. It is native to Eurasia and the Americas, where it is widespread and can be found in water bodies such as ponds, lakes, ditches, and streams. This is a perennial herb producing a thin, branching stem easily exceeding a meter in maximum length. The submerged leaves are linear to widely lance-shaped and up to 15 by 4 centimetres in length and width, respectively, while the floating leaves achieve shorter maximum lengths and are ovate or elliptic. Both floating leaves and submerged leaves are borne on long petioles, a distinguishing characteristic. The inflorescence is a spike of many small flowers arising from the water on a peduncle.
Potamogeton pusillus is a species of aquatic plant known by the common names small pondweed, lesser pondweed or least pondweed. It occurs in standing and slow-flowing freshwater habitats throughout the Northern Hemisphere.
Potamogeton compressus is a species of aquatic plant known by the common names grass-wrack pondweed, flatstem pondweed and eel-grass pondweed.
Oenanthe crocata, hemlock water-dropwort is a flowering plant in the carrot family, native to Europe, North Africa and western Asia. It grows in damp grassland and wet woodland, often along river and stream banks. All parts of the plant are extremely toxic and it has been known to cause human and livestock poisoning.
Oenanthe aquatica, fine-leaved water-dropwort, is an aquatic flowering plant in the carrot family. It is widely distributed from the Atlantic coast of Europe to central Asia.
Oenanthe fistulosa, tubular water-dropwort, is a flowering plant in the carrot family, native to Europe, North Africa and western parts of Asia. It is an uncommon plant of wetlands, growing around pools and along ditches, mainly in areas of high conservation value.
Oenanthe lachenalii, parsley water-dropwort, is a flowering plant in the carrot family, which is native to Europe and parts of North Africa. It is a declining plant of coastal wetlands.
Oenanthe silaifolia, narrow-leaved water-dropwort, is a flowering plant in the carrot family, which is native to Europe and adjacent parts of Asia and North Africa. It is an uncommon plant of water-meadows and wetlands.
Ranunculus baudotii, brackish water-crowfoot, is a flowering plant in the Ranunculaceae. As the name suggests, it tends to grow near the sea, typically in pools and ditches in coastal marshes that are slightly salty due to sea spray. It can also be found inland where there is some saline influence. It is not edible and has economic uses, but it is generally valued as a plant of conservation interest and an indicator of less agriculturally improved habitat.
Erodium lebelii, sticky stork's-bill, is an annual plant in the family Geraniaceae. It occurs on sand dunes and heaths on the Atlantic and Mediterranean coasts of western Europe. Its taxonomic status is uncertain: some authorities consider it merely a variety or subspecies of common stork's-bill while others consider it to be the same as the north African species Erodium aethiopicum.
