Preliminary report on a survey of Utricularia (Lentibulariaceae) in the Howard River – Shoal Bay area
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were found in the middle parts of the Howard River floodplain (Whitewood Rd to Gunn Pt Rd) and to the north of the Gunn Point Rd on the East Howard system. Utricularia leptorhyncha was found at two sites in the middle part of the Howard River floodplain (Girraween Rd to Gunn Pt Rd), but was recorded on Bathurst Island and incidentally at Litchfield NP during the time of the field work. Additional collections have also been made since 1992 (when the Leach et al study was published) in Charles Darwin NP, Kakadu NP and near the Elizabeth River - all significant additions to the known distribution of the species. Utricularia triflora was located at only one site during the survey, to the north of the Gunn Point Rd. However, during other field work in June, 2001 the species was recorded at three sites on the Sturt Plateau, one not far from Dunmarra extending the known range by almost 500 km. These and other collections made near Oenpelli, Maningrida and near the Goyder River over the past 5 years have greatly extended the known range of the species. It apparently has different habitat requirements than many other species, flowering after water receeds from the margins of flooded sandy swamps. Utricularia singeriana remains among the rarest of the Australian endemic Utricularia species found in the NT. It was not located during the survey despite being one of the more conspicuous species (C.Michell pers. comm.). It is know in NT from historical collections from 4 miles north east of Darwin which are now probably under suburban Darwin or the Darwin airport and from a recent collection from near Edith River. Species Richness and Habitat Species Richness. It was apparent that the more sandy sites with more open ground layer tended to have a greater number of species than did more clayey sites with a denser grass layer. Although the attached Utricularias all occurred in seasonally waterlogged habitats, the composition and richness of species on such sites appeared to be related to subtle variations in moisture and substrate conditions both in terms of micro and macro topography and in a temporal sense. Although limited data were collected on soil texture, the sand sheet Utricularias appeared to favour Melaleuca nervosa woodland with an open ground layer dominated by Dapsilanthus spathaceus on very sandy colluvium and obvious ground water seepage (e.g. U.dunstaniae, U.holtzei, and U.hamiltonii). The sandy sites with U.dunstaniae had the greatest number of species (mean = 8 species). As the density of the ground layer increased, usually with an increase in grasses and apparent higher soil silt or clay content, the number of species of Utricularia appeared to decline. Microtopography. On sandy sites, the distribution of sand sheet Utricularias on a site appears to be intricately connected to the system of hummocks and depressions (debil debil) caused through the activities of the terrestrial worm (???). In the seasonally swampy country they inhabit, these worms build low hummocks of soil a few cm or more high around the bases of Dapsilanthus or grass tussocks, apparently to maintain elevation above the surrounding water during the wet season. Typically U. dunstaniae, U.lasiocaulis, U. holtzei, U. capilliflora, and U. hamiltonii inhabit the shallow water (a few mm to a few cm deep) in the depressions whilst U.quinquedentata, U.chrysantha, U.odorata, U.caerulea and U.kamienskii inhabit the drier mounds (or the moist sand in areas that have already
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