Enkele zeldzame, taxonomisch problematische sieralgsoorten uit Het Hol

Mesotrophic quaking fen hollows in the Dutch nature reserve ‘Het Hoi’ (near Kortenhoef in the Province of Noord-Holland) harbour a rich desmid flora. Some rare, taxonomically problematic species are discussed separately. Pleurotaenium coronatum var. robustum and P. nodulosum, in former days mutually confused, are compared in their differentiating characteristics. Closterium didymotocum var. crassum is recombined to C. baillyanum var. crassum, principally based on the shape of its cell apex. It cannot be totally excluded, however, that the taxon in question has to be considered a mere anomalous form of C. baillyanum var. baillyanum. A Closterium-species that could not be identified in a satisfying way shows much resemblence with C. macilentum, except that girdle bands are lacking

Bijdragen tot de kennis der Nederlandse Desmidiaceeënflora

The bogs and broads situated in the NW corner of the province of Overijssel contain a rich desmid flora. Some species rare in or hitherto unrecorded for the Netherlands are discussed. The occurrence of a number of species with a predominantly arctic-alpine distribution, viz. of Cosmarium anceps, C. holmiense var. integrum, C. speciosum, and C. crenatum, is rather striking. These species live, in the area studied, atmophytically among bryophytic vegetation in mesotrophic quaking bogs. Also notable is the common occurrence of the not very well known species Cosmarium insigne in the tychoplankton of many lakes, particularly in those with well-developed stands of Stratiotes abides

Bijdragen tot de kennis der Nederlandse Desmidiaceeënflora, 3. N.W.-Overijssel (2)

Subsequent to a previous publication (COESEL, 1974), an additional number of noteworthy records of desmids from the NW corner of the province of Overijssel is reported. The complex of Holocenic lakes and peatbogs of that area increasingly proves to be the richest site of desmids in the Netherlands at the present time. It is especially the very shallow, mesotrophic pools in quivering bogs which have repeatedly yielded records of species new for the Dutch desmid flora (such as Cosmarium hornavanense var. dubovianum, C. quasillus, and C. subbroomei). It is to be regretted, however, that there are clear indications of a depauperisation of the tychoplanktonic desmid flora owing to a deterioration of the waterquality. Some species in particular, such as Cosmarium insigne (compare COESEL, 1974) and Staurastrum gladiosum var. delicatulum, which were till recently quite common in old peat pits in the area under discussion, exhibit clear indications of a decrease in population density

Bijdragen tot de kennis der Nederlandse Desmidiaceeënflora, 2. Desmidiaceeën uit het Mosterdveen

The Desmidflora of the Mosterdveen (a complex of small fen soaks in the Netherlands province of Gelderland) provides a good example of a microphyte cenose characteristic of an oligotrophic type of water (as described by BEIJERINCK, 1926), which has in the meantime become very rare. The most typical indicator species found in the Mosterdveen are Cosmarium ralfsii Bréb., Micrasterias jenneri Ralfs, Euastrum crassum (Bréb.) Kütz., and Xanthidium armatum (Bréb.) Rabenh. Some species whose occurrence and distribution in the Netherlands is not so well known, partly owing to their problematic taxonomy, are discussed separately

Bijdragen tot de kennis der Nederlandse Desmidiaceeënflora 4. De leemputten bij Staverden

Near Staverden (province of Gelderland) there is a moist heath where a calcareous loam is found mostly very close to the surface. In the past the loam was exploited in several places, which resulted in an unevenness of the terrain and in a number of gradients (wet-dry, rich in humus — poor in humus, lime-rich — poor in lime). The more or less permanently waterfilled loam pits contain a rich desmid flora characteristic of a mesotrophic environment. Among the taxa recorded from this locality four are new for the Netherlands, viz., Staurastrum sexcostatum var. productum, Cosmarium annulatum, C. decedens var. apertum, and C. notabile. Of common occurrence in more oligotrophic shallow depressions filled with Sphagnum found at other sites in the area are, e.g., Staurastrum arnellii and its var. spiniferum. We agree with MESSIKOMMER (1929) in doubting whether these two taxa indeed represent one species. The ‘typical’ variety of S. arnellii may well belong in the affinity of S. muricatum and S. hirsutum, whereas the var. spiniferum rather belongs near S. scabrum

Subatmofytische sieralgsoorten, nieuw voor de Nederlandse flora

In de afgelopen jaren kon een viertal sieralgsoorten als nieuw voor de Nederlandse flora worden vastgesteld: Mesotaenium caldariorum, Actinotaenium pinicolum, Cosmarium pericymatium en Staurastrum habeebense. De standplaatsen van waaruit deze soorten verzameld werden, zijn voor sieralgen ongebruikelijk, te weten een regenpijp, een droge veenmosbult, een stenen tuinornament en een betonnen havenhoofd. Buiten Nederland staan genoemde soorten bekend als (zeer) zeldzaam. Aangezien genoemde habitats tot voor kort niet of nauwelijks specifiek op sieralgen zijn geïnventariseerd, mag echter verwacht worden dat de hieronder besproken soorten minder zeldzaam zijn dan tot voor kort werd verondersteld. Four desmid species, Mesotaenium caldariorum, Actinotaenium pinicolum, Cosmarium pericymatium and Staurastrum habeebense were found to be new to the Dutch flora. They were found in quite unusual habitats, i.e., a rain-pipe, a dried Sphagnum hummock, a stone garden ornament and a concrete harbour platform, respectively. The desmid species mentioned above are also known to be (very) rare outside of the Netherlands. However, because the above-mentioned habitats have been little investigated for desmids, more records can be expected