Morphological comparison of some riverine Batrachium species

Genus Batrachium (DC.) Gray is evolutionary young but very important group of aquatic plants. It is very essential component in the river for its ability to affect flow dynamics, silt deposition and provide refuge for ecologically important macroinvertebrate and fish populations and can be considered as the indicator of the sustainability of riverine ecosystem. Communities with Batrachium species are regarded as significant for European Union and listed in Apendix 1 of Habitat Directive (code 3260). Plants of this genus are important not only from the scientific point, but also and in terms of plant conservation. By reason of this, studies of morphological features of Batrachium species are very relevant. Our study is an introduction to further detail research of Batrachium species. It was performed in 16 river catchments. During this studies 185 Batrachium individuals were collected and measured. The morphological features such as the presence of floating leaves, number of capillary leaves furcations, length of terminal leaf segments, length of petiole, hairiness of stipules, length and number of petals, and hairiness of receptacle, were used in this analysis. The species level taxonomic identification of the individuals was performed using keys after Cook (1966), Webster (1988), Dahlgren, Jonsell (2001), Bobrov (2003), Webster, Rich (1998). Nonparametric Kruskal-Wallis test was used to compare morphological features. Mann-Whitney U test was used to identify differences between specific populations. The analysis showed that not all analysed features were uniformly important in Batrachium species identification. Acording to some morfological features all samples were grouped in two groups. Individuals from the first group distinguished glabrous or sparse hairy receptacle, had 5-8 petals (length ranged from 0.4 to 1.1 cm), had only capillary leaves, length of secondary leave ranged from 4 to 9 cm, and length of the sixth leave ranged from 6 to 12 cm. While specimens from another group had densely pubescent receptacle, five petals (length ranged from 0.2 to 0.5 cm), length of secondary capillary leaves ranged from 3 to 7 cm and length of the sixth leave ranged from 5 to 8 cm. Some individuals from Skroblus, Ūla and Merkys populations had intermediate leaves. We suppose, that individuals from first group can be described as Batrachium fluitans, whereas plants from second group – as Batrachium penicillatum s.l. or Batrachium trichophyllum.