Analele ştiinţifice ale Universităţii „Al. I. Cuza” Iaşi Tomul LVII, fasc. 1, s. II a. Biologie vegetală, 2011 VASCULAR FLORA OF THE DANUBE DELTA V. CIOCÂRLAN* Abstract: The aim of this paper is to present an updated list of the vascular flora of the Danube Delta, together with endangered categories, in accordance with the International Union for Conservation of Nature (IUCN). Also, the flora’s categories are presented according to ecological and habitat criteria. Keywords: vascular flora, Danube Delta, IUCN. Introduction The Danube Delta is Romania’s youngest relief unit and the territory with the greatest habitat diversity and as a consequence with an impressive taxonomic diversity. On a relatively limited area of 3,466 km2 [10] representing 1.5% of the Romanian territory, live around 1,000 vascular plant species, almost 1/3 of all the species of the Romanian flora. Short history of floristic research The Danube Delta’s vascular flora1 has drawn the attention of many scientists. Different groups of plants related to different habitats (such as water, swamps, pastures, sands, salty areas), plants that are important for fishery or wooden plants are described in over 300 scientific articles published so far. Other articles record taxons that are new to the Romanian flora. There are also many papers on vegetation where species found in different associations are published. Below are listed the main authors that researched and published synthesis articles on the Danube Delta’s flora. The authors are mentioned in the chronological order and in the bibliography additional data can be found: Kanitz A. (1879-1881), Brândză D. (1898), Grecescu D. (1898, 1909), Pallis M. (1916), Panţu Z. and collab. (1935), Prodan I. (1935-1939, 1939), Borza Al. (1947, 1949), Săvulescu Tr. (edit.) (1952-1976), Beldie Al. (1977, 1979), Dihoru Gh. and Negrean G. (1976), paper with a rich bibliography - 228 titles, Şeliag-Sosonko, Dubîna (1984), paper refering to the flora of Chilia’s secondary delta, Ciocârlan V. (1994, 2000, 2009). Materials and methods Before presenting the flora’s categories according to ecological and habitats criteria, the following explanation is necessary: - we will only refer to species living in the actual Delta; - all commentaries target species recorded in the last 30 years and which exist at least partially as a documentary material in the herbariums BUAG *University of Agronomical Sciences and Veterinary Medicine of Bucharest, B-dul Mărăşti nr. 59, Sector 1, Bucharest, Romania. 1 We use the term – Vascular flora – in accordance with the English, French and German botanical literature. 41 (University of Agronomical Sciences and Veterinary Medicine of Bucharest), I (“Al. I. Cuza” University of Iaşi) and IAGB (Botanical Garden of Iaşi University); - as the publication of an annex volume comprising the complete list of species is envisaged, in this first part we will focus on the main species that determine plant associations, species that are characteristic to certain habitats, trying to anticipate their future evolution; - in the presentation of the flora categories, we must consider the great capacity of plant species to adapt to the ecological factors, which makes possible for one species to be recorded in different ecological groups with two or three step variation. Example: mesophilic-hydrophilic species or resistant halophilic-preferant halophilic species or psamofilic-calcareous species or neutral-moderately acidophilic species etc. Results and discussions Aquatic Flora (Hydrophyta) The water as an ecological factor induces a relative uniformity of the flora. However there are obvious flora differences determined by other factors that lead to the formation of different habitats with their own species. Thus the aquatic flora shows differences according to the type of water – fresh or salty, running or stagnant, the degree of mineral or organic clogging, the levels of pollution, eutrophication or oxygenation, etc. The flora of the fresh running waters is represented by few but nummerically abundant species that are living on streams and channels with reduced water flow, while on the Danube’s branches and on the channels with an active water flow the vascular species are either lacking or are present only on the shores. Along the streams and channels where the clogging phenomenon and accumulation of decaying organic matter are present the following species thrive: Stratiotes aloides, Hydrocharis morsus-ranae, Utricularia vulgaris, which are floating species during anthesis, as well as fixed species, such as: Hippuris vulgaris, in shallow eutrophic waters, Hottonia palustris, sparsely seen lately, Potamogeton pectinatus very frequent, living in stagnant low-salted waters, Nymphoides peltata, Vallisneria spiralis, etc. We mention that these species also live in small lakes with slow water circulation. The flora of the fresh stagnant waters. The species living in lakes are different depending on the lakes’ characteristics, firstly on the lake’s size and on the water exchange level. There are the so-called open pools (lakes), which are lakes having a spread acvatorium, with natural active water exchange, and the closed pools (lakes) which are smaller and with a slow water circulation. The open lakes (pools) are subjected to the action of winds, water bottom currents, the water is well-oxygenated, while the aquatic plant species, as well as the submerse plant species, fixed or not, are scarce and found towards the lakes' shores, where they are protected by the taller helophilic species, primarily by the reed (Phragmites australis). 42 The closed lakes (pools) are smaller, less exposed to winds and less influenced by currents, and as a consequence in these habitats the processes of clogging, sedimentation and organic matter’s decaying are predominant. These processes are favoring the development of a very rich immerse and submerse flora, floating or fixed. The hydrophilic species have a very large area, some are cosmopolitan, others are circumpolar, Eurasian, European and a few are adventive. Hydrophilic species with a reduced living area, specific to the Danube Delta, are not known. There are few taxons, recently discovered in the Delta, whose complete spreading within the Delta is not yet known. Such species are: Lemna minuta and Trapa natans subsp. muzzanensis known only in the vicinity of the Nebunu Lake. Otherwise, Elodea nuttalli is frequent throughout the entire Delta and has replaced in great part Elodea canadensis which has become a rarity. Ceratophyllum demersum and Potamogeton pectinatus are also well represented, as well as Elodea nuttallii, which show an explosive spreading as a result of the eutrophication. Species mentioned as frequent by the old literature [9] became rarer: Aldrovanda vesiculosa, Ceratophyllum submersum, Hottonia palustris, Marsilea quadrifolia, and according to some observations even Trapa natans has dissapeared from such lakes as Roşu, Roşuleţ, Puiu, Fortuna [15]. Since a second volume (annex) will be published with a complete list of vascular species and taking into account the large spreading of the hydrophilic species, well known to the specialists, we mention the existence throughout the entire Delta of species belonging to the following genera: Potamogeton, Myriophyllum, Nymphaea, Utricularia, etc. The flora of the brackish and salty waters is very poor as in the inner Delta there are only fresh water lakes. However, Najas marina was recorded in the Răducului Lake, a species that is facultative halophitic or tolerant to salinity. We mention that the pH of the lake is of 8.02. Also, in the north-east of the Sinoe Lake, close to Gura Portiţei, was recorded Ruppia cirrhosa [7], a halophilic species new to the Romanian Flora. We emphasize that the Sinoe Lake is connected to the sea waters. Zannichellia palustris subsp. pedicellata, a halophilic taxon, is mentioned from the Sinoe and Goloviţa Lakes, that are influenced by sea waters [9]. Higro-helophilic flora (Hygro-helophyta) This is the most spread flora category within the Danube Delta and is represented by a large number of species with numerous individuals. This type of flora lives on lake shores, channels and streams, in shallow pools and even on areas that are periodically flooded, but with permanent water to the root system during the drought periods. The alluvial layer is rich in nutritive substances, dead plant organs (rhizomes, roots) in different stages of decomposition. By the accumulation of dead undecomposed organs, a new layer isolating the contact of the living roots with the bottom alluvia is formed and these roots get fixed in this layer. Through the action of the wind and of the resulting waves, pieces of the isolating layer become detached from the bottom, start floating and form islets known as “plaur”. The higro-helophilic species have a large range, as the hydrophilic species, the majority being circumpolar and Eurasian. Few species have a reduced range, such as: Carex elata, with an European area, forming dense large bushes, more or less cylindrical, known as “popândaci”. 43 Within the Danube Delta were recorded and published [7] a few adventive species: Bidens connata, B. frondosa, B. vulgata, Cyperus odoratus, Lindernia dubia, Sagittaria trifolia. Other floristic novelties for the Romanian flora, recorded within the Danube Delta are: Achillea innundata and Eleocharis mitracarpa, that are Pontic species, and Cladium mariscus subsp. martii [7]. Rare species are: Limosella aquatica, only in Meleaua Sacalin, Angelica