Tubular Water-dropwort

Tubular water-dropwort is a hairless, stoloniferous perennial growing up to 80 cm tall with brittle, hollow, inflated cylindrical stems 0.5 cm in diameter, which are constricted at the nodes (hence the specific name fistulosa). Unlike some other water-dropworts, it has no swollen tubers among the roots, but it can reproduce vegetatively by the lengthy stolons. The leaves vary widely in shape, with the upper ones being typically pinnate and having narrow, almost linear segments, while the lower ones can be 2- or even 3-times pinnate, with broader, flat leaflets, more like those of other umbellifers. The leaf stalks of the upper leaves are fistular, like the stem, and longer than the pinnate leaf blade. It flowers between July and September in northern Europe, with clusters of 2-4 umbels about 1 cm in diameter, each of which has numerous white to pinkish flowers. A distinguishing feature is that, unlike many other umbellifers, it has no bracts but only small bracteoles on the individual umbels. The rays (stalks to the umbels) are 10–30 mm long and become thicker after flowering. Plants are monoecious, with hermaphroditic and male flowers on the terminal umbels, and only male flowers on the lateral umbels. Each flower has 5 unequal petals with the larger, outer ones radiating, 5 stamens and 2 prominent styles arising from a swollen base (stylopodium) at the top of the ovary. …

The global range of tubular water-dropwort is from Europe through the northern half of Africa to western parts of Asia. It occurs no further north than southern Scandinavia and is rare as an introduction beyond its natural range. In Britain and Ireland it is found mainly in the lowland eastern counties, becoming increasingly rare towards the uplands of the north and west. In France the pattern is similar, with the main populations in the southern lowlands, becoming rarer towards the upland regions around the Alps. The IUCN threat status is Least Concern (LC) (as assessed in 2013), both globally and in Europe. In France, it is similarly considered unthreatened nationally, but in some reasons it is declining, notably in Limousin, where it is Critically Rare (CR), and Midi-Pyrénées, where it is Endangered (EN). It is also declining in some other European countries, such as Slovenia, where it is classed as EN. In Britain it is classified as Vulnerable (VU), while in England it is believed to have declined by 35% in its area of occupancy between the 1960s and the 1990s. This decrease appears to have continued in some English counties, such as Kent, where the number of sites has shrunk by 60% between the 1970s and 2005, despite it being a Biodiversity Action Plan species.

It is a wetland plant, occurring naturally in swamps and marshes along valleys and in river deltas such as the Camargue in France and the Doñana National Park in Spain. In well-drained agricultural landscapes it is now more likely to be found in drainage ditches, farm ponds and grazed wet meadows. In some places it is found as a halophyte in coastal dune slacks or brackish grazing marshes, as at Aiguamolls de l'Empordà in Spain or on the Sefton Coast in Britain. It favours clean, mesotrophic water, slightly base-rich conditions, and moderately high light levels, which make it an axiophyte in most British counties. In France it is an indicator of the Gratiola officinalis-O. fistulosa community in restored wetlands along the Saône river. In contrast, it is dominant in a type of flooded creeping bent meadows on clay in Italy, in a Ranunculus ophioglossifolius-O. fistulosa community.

In places where it has noticeably declined, attempts have been made to restore its habitat. Wet meadows were sown in the valley of the Meuse in NE France, but after three years it had not colonised them. However, when a species-poor ditch in an area of arable farmland in Romney Marsh was cleared and planted up, O. …

Tubular water-dropwort roots have been found to contain small quantities of Oenanthotoxin, the toxic agent that makes hemlock water-dropwort so dangerous. However, the quantities are much (10 x) lower and it is generally considered safe, or even palatable. Oenanthe fistulosa is freely grazed by livestock. It is used in traditional medicine in Algeria and investigations into the essential oil show there are constituents that could have medical benefits as well as a chemical, Heneicosane, which attracts mosquitoes involved in transmitting Dengue fever. It has been reported as part of the traditional cuisine in parts of southern Italy and Turkey, where it is known as Gazyak or Kazayağı (a general name for various species of water-dropwort), and the basal leaves are cooked as a meal. The Irish botanist D.E. Allen suggests that O. fistulosa might be the plant that was reported in County Wicklow as a treatment for rheumatism.

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