Ulva intestinalis is a conspicuous bright grass-green seaweed, consisting of inflated irregularly constricted, tubular fronds that grow from a small discoid base. Fronds are typically unbranched. Fronds may be 10-30 cm or more in length and 6-18 mm in diameter, the tips of which are usually rounded. Like other members of the genus, Ulva intestinalis is a summer annual, decaying and forming masses of bleached white fronds towards the end of the season.

Link for (Pereira, 2010) Handbook Guide

Original publication: Linnaeus, C. (1753). Species plantarum, exhibentes plantas rite cognitas, ad genera relatas, cum differentiis specificis, nominibus trivialibus, synonymis selectis, locis natalibus, secundum systema sexuale digestas. Vol. 2 pp. [i], 561-1200, [1-30, index], [i, err.]. Holmiae [Stockholm]: Impensis Laurentii Salvii.

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Adjective (Latin), relating to or found in the intestines

Digenetic, isomorphic alternation of generations (sporophytes and gametophytes).

Species of the genus Ulva are rapidly growing opportunists, favoured by the frequency and speed of their reproduction. The short lived plants reach maturity at a certain stage of development rather than relying on an environmental trigger. Ulva intestinalis can be found in reproductive condition at all times of the year, but maximum development and reproduction occur during the summer months especially towards the northern end of the distribution of the species (Burrows, 1991). The life history consists of an isomorphic (indistinguishable except for the type of reproductive bodies produced) alternation between haploid gametophytic and diploid sporophytic generations, but can be modified by environmental conditions (Burrows, 1959; Moss & Marsland, 1976; Reed & Russell, 1978). McArthur & Moss (1979) examined the process of gametogenesis and gamete structure using scanning and transmission electron microscopy.

The haploid gametophytes of Ulva produce enormous numbers of biflagellate motile gametes which cluster and fuse to produce a sporophyte (diploid zygote). The sporophyte matures and produces by meiosis large numbers of quadriflagellate zoospores that mature as gametophytes, and the cycle is repeated. Both gametes and spores may be released in such quantities into rock pools or slack water that the water mass is coloured green (Little & Kitching, 1996). Together spores and gametes are termed 'swarmers'. Swarmers are often released in relation to tidal cycles, with the release being triggered by the incoming tide as it wets the thallus. However, the degree of release is usually related to the stage of the spring/neap tidal cycle, so allowing regular periodicity and synchronization of reproduction (Little & Kitching, 1996). Christie & Evans (1962) found that swarmer release of Ulva intestinalis (as Enteromorpha intestinalis) from the Menai Straits, Wales, peaked just before the highest tides of each neap-spring cycle.

Mobility of swarmers belonging to Ulva intestinalis (as Enteromorpha intestinalis) can be maintained for as long as 8 days (Jones & Babb, 1968). Algae such as Ulva intestinalis tend to have large dispersal shadows, with propagules being found far from the nearest adult plants, e.g. 35 km (Amsler & Searles, 1980)

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Hayden, H.S., Blomster, J., Maggs, C.A., Silva, P.C., Stanhope, M.J. & Waaland, J.R. (2003). Linnaeus was right all along: Ulva and Enteromorpha are not distinct genera. European Journal of Phycology 38: 277-294.

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In Portuguese: Alface-do-mar

In English: Gut weed, Gut laver, Hollow Green Weed.