Acta Botanica Neerlandica 8 (1959) 247-256

The Batrachospermeto-Chaetophoretum,

A Remarkable Algal Association

in the Netherlands

C. den Hartog

(Goes)

(received March 12th, 1959)

In 1949 Westhoff called attention for the first time to the re-

markable submerged algal growth of Batrachospermum moniliforme and

Chaetophora incrassata on stalks of reed and Typha, observed in a fragment of the Scirpeto-Phragmitetum in Botshol, a small lake near the village of Abcoude.

“Dc onder stengels van Phragmites en Typha water zijn een

dankbare standplaats voor plantaardig “lasion” of wel aangroeisel

in de vorm van interessante en vaak zeer fraaie blauw-, rood- en

groenwieren, waarvan sommige wellicht min ofmeer kenmerkend

voor associatie ofverbond zullen blijken te zijn: ik noem Batracho- der inlandse die niet in spermum sp., een weinige roodwieren, uitgesproken brak of zout water leven, het puimsteenachtige, met kalk geincrusteerde groenwier Chaetophora incrassata fo. crystal- lophora. de blauwwieren Rivularia dura, Phormidium laminosum, Schizothrix coriacea, etc.” x )

I have studied this algal vegetation also in various ponds and pools,

and I found it representing a rather constant association with probably

a wide distribution: the Batrachospermeto-Chaetophoretum. It appeared,

however, that this association is by no means a characteristic epiphytic it . community, for also occurs on stones and live The nomenclature used for the algae follows Pascher, Siisswasser-

fiora. and desmids have not been studied.

Floristic composition

The Batrachospermeto-Chaetophoretum is highly characterized by the combination of Batrachospermum moniliforme and Chaetophora incrassata. The first , however, is characteristic for the association only in

the it in stagnant waters of ponds and lakes; in streams occurs a quite other then with the vegetation and is often allied moss Platyhypnidium rusciforme (Neck.) Fleisch. (Oxyrrhynchietum rusciformis, Gams, 1927; vide

von Hübsghmann, 1953). Israelsson (1942) considers it as a rather

“The of and form habitat b submerged stalks Phragmites Typha a very suitable for vegetable lasion in the form of interesting and often beautiful Cyanophyceae,

Rhodophyceae and Chlorophyceae, some of which may be perhaps more or less characteristic for association (Scirpeto-Phragmitetum) or alliance (Phragmition): I mention of the few native red which do live in Batrachospermum sp., one algae, not brackish salt or water, the pumiceous, lime-incrusted green algaChaetophora incrassata fo. the Rivularia crystallophora , bluegreen algae dura, Phormidium laminosum, Schizothrix coriacea etc.” (Transl. author).

247 248 C. DEN HARTOG

TABLE I

Batrachospermeto-Chaetophoretum

Number: 1 2 3 4 5 6 7 8 9

Covering in %: 10 30 5-10 60 65 40 40 40 50

1 3 2 1 Batrachospermum moniliforme . + 2 2/3 + 2 incrassata 3 Chaetophora .... 1 + 2 2 3 2 2 2

— — — — — — Chaetonema irreguläre .... + + +

Cladophora glomerata + + + 1 2 + 2 — 2

— — 1 + Oedogonium sp + + + + +

— + — — Spirogyra sp + + + + +

— — — — Mougeotia sp + + + +

— — — 1 — — 2 Tolypothrix lanata + 1

Ophridium versatile — — +/1 — + + — + —

Draparnaldia plumosa 2 + — + — — — — —

; biasolettiana — — — — + + — + Rivularia ....

Euspongilla lacustris + +/1 + — — — — — —

— — 1 — — — — — Enteromorpha prolifera .... +

— — — — — Coleochaete scutata + — — +

— — — — — — — Ophiocytium parvulum .... + +

Nostoc sphaericum — — — — + — — + —

— — — — — — — Schizochlamys gelatinosa . . . 1 +

— — — — Bulbochaete — — — + + sp

Ophiocytium maius — — — — — — — + +

— Stigeoclonium tenue — + — — — — — —

— — — — — — — Phormidium tenue + —

Cordylophora caspia — — + — — — — — —

— — — — — — — — Hydra vulgaris attenuata . . . +

— — — — — — — —

Phormidium tinctorium .... +

Dichothrix baueriana — — — — — — — + —

Chlorococcum wimmeri — — — — — — — — .... +

Microcystis aeruginosa .... +

Legenda:

Botshol 1. Prov. of Utrecht; near Abcoude, ca. 15 km south ofAmsterdam. Brugge- sloot, on reedstalks along the bank, opposite to the farm of Mr. M. Verwey. Lasion of incrassata and Balrachospermum moniliforme, Chaetophora many specimens 2 of 1 40 CP-content Draparnaldia plumosa. Surface: m ; depth cm; 842 mg/1; 27-V-’56; CH 56016 A.

2. Botshol, in a small pool between the Bruggesloot and the Kleine Wije, and

connected with these waters. Beautiful Balrachospermum-growth on the submerged and found parts of Phragmites Typha-stalks, but only on the mown stalks, not the Surface: 10 2 on juvenil shoots. Very sheltered station. m ; depth 30-50 cm; CP-content in March 1956: 450 mg/1; 24-III-’57; CH 57004. 3. in the south-western of the Grote stalks Botshol, part Wije on mown Typha- and bottom on pectinatus; covered by Chara hispida. Epiphytic vege- tation of and 5 a Chaetophora Batrachospermum. Surface: m ; depth 80-100 cm; CP-content in March 1956: 479 mg/1; 24-III-’57; CH 57005. sheltered small connected with north of 4. Botshol, very pool the Vliet, ca. 100 m

the large willow tree, with a community of Nymphaea alba, Utricularia vulgaris On reedstalks and Phragmites. a luxuriously developed Batrachospermum-Chaeto- phora-growth, in which brown clods of diatoms are covering 40-50 %. Surface: 1 2 50-80 Cl'-contcnt in March 1956: in m ; depth cm; very variable, 392 mg/1, June 1956: 1123 mg/1; 16-VI-’57; CH 57009.

5. Prov. of North Holland; Naardermeer, between the towns Weesp and Naardcn,

ca. 20 km east ofAmsterdam; Side-ditch ofthe Hoofdtocht, west of the Machine- TOE BATRACHOSPERMETO-CHAETOPHORETUM 249

tocht. Very fine Chaetophora-Batrachospermum-vegetation on reedstalks. Surface:

2 2 m ; depth 50 cm; 30-V-’54; CH 54044. in ditch the 6. Naardermeer; a nearly closed by vegetation, parallel with Hoofd- tocht, between Spookgat and Grote Meer. Extremely sheltered station with

beautifully developed Hydrochareto-Stratiotetum. On reedstalks a dense Batracho- Surface: 2 2 45 CH 57007. spermum-Chaetophora-vegetation m ; depth cm; 2-VI-’57;

7. Prov. of Utrecht; Oud Loosdrecht, ca. 8 km west of Hilversum, along the bank of the Loencrveense Plas. Well-developed vegetation of Chaetophora incrassata,

Batrachospermum moniliforme and Cladophora glomerata, on stones, heavily shaded by

2 Scirpus lacustris and Salix sp. Surface: 1 m ; depth 20-30 cm; 10-VII-’55; CH 55035.

8. Prov. of North Holland; Petten, pool in the dune valley Rietput with dense vegetation of Characeae, Potamogeton natans and P. gramineus. On stalks of

reed and Carex luxurious incrassata-lasion. Surface; 3 2 lasiocarpa a Chadophora m ; CH depth 20-40 cm; 22-V-’54; 54029. 9. Prov. of South Holland; Island of Voorne, Quackjeswater. Fine Chaetophora- shaded the Batrachospermum-vegetation in a station along bank, on submerged

2 and Surface: 1 40-50 branches, Phragmites- Typha-stalks. m ; depth cm; 23-V-’54; CH 54030. indifferent species, occuring in different kinds of water, not related to the amount of electrolytes. In the Netherlands, however, it shows a distinct preference for eutrophic and mesotrophic ponds; it is absent in from waters poor electrolytes. Chaetophora incrassata has its optimum in this association but cannot exclusive because it be found also be considered as an species, may in the Cladophoretum glomeratae lacustre. In running water, however, it is

rare. The collected in very only specimens, slowly flowing water, present in the Rijksherbarium, have been found by Spree near Lochem (12-IV-1860). Luther (1953) who mapped the distribution

of the species in Scandinavia, discovered a remarkable preference for

areas rich in lime. Chaetophora occurs also occasionally in oligohalinous

1 the water ), so dependence from lime is not certain. It is clear, however,

that the species needs a high concentrationofelectrolytes. The maximal

tolerated in nature was 2.1 to Waern salinity °/ 00 Cl', according (1952). These findings ofScandinavian investigators, hold also for the

Dutch waters, where I found theassociation to be common in eutrophic and freshwater well in with mesotrophic as as oligohalinous water a

to Cl'. It tolerates of the water well, salinity up 1,3 °/ 00 pollution very but observed in industrial The it was not yet sewage. hemisphaerical

juvenil stages of the species often have been confounded with Chaeto- phora elegans and Ch. pisiformis. minute Chaetonema irregulare is a epiphytic alga, occurring on in Chaetophora as well as on Batrachospermum the gelatinous layer around

the stems; however, it is difficult to discover. Although it is presented 3 times in the it nevertheless be of only table, may a species common

occurrence.

In addition to the characteristic of the association the species green

alga Cladophora glomerata and the bluegreen alga Tolypothrix lanata are

l The of amounts to 0-0,3 Cl'. For ) chlorinity °/00 oligohalinous and these mesohalinous water values are and a respectively 0,3-l,6°/ 00 1,6-9 10 Cl' of °/ 00 (System Valikangas-Remane). 250 C. DEN HARTOG

often abundant. Contrary to Batrachospermum, Cladophora glomerata the illuminated in the association. It is prefers most spots very übiqui-

tous and dominates in very different vegetations, viz. in the Clado-

the phoretum glomeratae lacustre, in meso- to polyhalinous Cladobhoreto-

Polysiphonietum den Hartog, n.p.), and) in the rheophilous Cladophoreto -

Lemaneetum (= Cladophoretum glomeratae rheobenthicum Symoens, 1957). mountainous Even in the Hydruretum foetidi it sometimes may dominate. and and Tolypothrix lanata, more rarely T. tenuis T. distorta, too, form beautiful the coloured bushes on reedstalks. Other companions of the

association, rather inconspicuous, but nevertheless always present in

less are and Oedo- more or large quantities, Spirogyra sp., Mougeotia sp.

I found them in sterile state. gonium sp. However, always a Further Rivularia biasolettiana (incl. R. dura) is a common species,

occurring on reedstalks, wood, Chara hispida, Potamogeton pectinatus and

stones. This species is also abundant in the Cladophoretum glomeratae lacustre. Also the large brightgreen colonies of the Ophridium versatile Ehrb. be found all substrates but may on imaginable they prefer hydrophytes as Potamogeton and Chara for attachment. in Coleochaete scutata occurs small numbers on Typha- and Phragmites-

stalks, but is much more abundant on the undersurface of the leaves

of Nymphaea alba, Nuphar luteum and Stratiotes aloides.

More or less characteristic for eutrophiated waters are Stigeoclonium tenue and Draparnaldia plumosa. They have been found in the Batracho- spermeto-Chaetophoretum along the banks of frequently used ditches between the meadows, in ponds and pools connected with them, and in the of farms. Last mentioned tolerates vicinity species very large fluctuations in salinity.

In oligohalinous waters Enteromorpha prolifera is often abundant in

the association. This species, however, reaches its optimum in the

meso- and polyhalinous Enteromorphetum prolifero-intestinalis, where it often is the dominant species (den Hartog, n.p.). Diverse bluegrecn

in I algae occur frequently the association. collected Dichothrix Nostoc Oscillatoria baueriana, Microcystis aeruginosa, sphaericum, amphibia,

Phormidium laminosum, P. tenue, P. tinctorium and Schizothrix coriacea.

Probably this list can be enlarged.

In the samples of the Batrachospermeto-Chaetophoretum from the dune-

I found also Bulbochaete and pools Schizochlamys gelatinosa, sp. Ophio-

cytium maius. These species are reported to occur in the other lakes

but in investigated, were absent the samples studied by me.

Synecology

The association occurs in clear freshwater under eutrophic and

mesotrophic conditions. In the oligohalinous water of Botshol it is exposed to considerable annual fluctuations in chlorinity. In spring

amounts to 0,3-0,5 ; in summer it increases to 1,1—1,3 chlorinity °/ 00 °/ 00, decreasing again in autumn. In theother localities investigated chlorinity

is low. In the Naardermeer it amounts to in eutrophic 0,05-0,14 °/ 00, the Loenerveense plas to 0,03-0,04 in the mesotrophic °/o 0, dunepools

and to Rietput 0,1 °/ . Quakjeswater 00 THE BATRACHOSPERMETO-CHAETOPHORETUM 251

The association the of old stalks mostly occurs on submerged parts and roots of Phragmites, frequently also on Typha stems, more rarely on Equisetum fluviatile, Potamogeton pectinatus, P. compressus and Chara In the and globularis. addition to epiphytic occurrence epilithic epizoic growth were also observed. I found beautiful examples of the associ- ation on shells of live Limnaea stagnalis (L.) and Planorbis corneus (L.), so the minimum area of the community is very small. As stones are dumped only in localities exposed to wave-action, where the Batracho- does the association is in spermeto-Chaetophoretum not occur, our country mainly epiphytic.

The in rather Batrachospermeto-Chaetophoretum occurs shaded localities where too small for the quantities oflight penetrate very photophilous Cladophoretum glomeratae lacustre. In the Loenerveense Has near Oud

Loosdrecht, where both communities occur together, I only found the

Batrachospermeto-Chaetophoretum on stones, heavily shaded by Salix- shrubs along the banks of the pond, the light from the other side being intercepted by dense facies of Scirpus lacustris. In reedborders the habit of the association sciaphilous causes a very the remarkable distribution on algal vegetation. On the most exposed, outermost stalks of the reedborder the Batrachospermeto-Chaetophoretum is absent from 0-15 cm below the water level, and has been replaced

Fig. 1. Transsect of a reedborder.

1 = Omphalia belliae, 2 = Cladophora

glomerata- facies,I 3 =Batrachospermeto-

4 = of Chaetophoretum, coenose Cordylo- phora caspia and Euspongilla lacustris. 252 C. DEN HARTOG by Cladophora glomerata, rarely accompagnied by other algae in this habitat. below In a depth -15 cm the fragile Batrachospermum plants and the brightgreen bushes of Chaetophora incrassata appear. In clear water they descend to 70-80 cm, rarely to 1 m depth in the outside of the reedborder. More inward in the reed-edge, where the of the limit of the association coincides quantity light decreases, upper with the water level, while the lower limit may be reached already at

30 cm depth. The lower limit of the association is often determined by with in which the competition zoocoenoses, hydroid Cordylophora caspia the mussel Dreissena and the (Pall.), polymorpha (Pall.) sponges Euspon- gilla lacustris (L.) and Ephydatia fluviatilis (L.) are leading forms. On

the reedstalks in Naardermeer and Botshol a narrow belt of the fungus

belliae be found above the water level in Omphalia Johnst. may slightly autumn. A scheme of the zonation in reedborders is given in Fig. 1.

Life cycle

The annual rhythm of the association has been studied from 1954 to 1957 in Botshol. Here incrassata few weeks after Chaetophora appears a disappearance of the last ice, thus generally speaking in March.

in is The species soon increases numbers and it common during

In it spring and summer. October and November dies. Occasionally individuals in winter some hemisphaerical, 1-2 mm large may be found. the whole Batrachospermum moniliforme occurs during year, and live several after the ice probably may years. Immediately melting of which be found to In gonimoblasts are formed, may halfway May.

summer and autumn gonimoblasts have been found only exceptionally. In the be in the May everywhere germlings can found; they grow out

of the to blackish or bushes. The course year very large, greenish

largest plants, found by me, measured up to 25 cm, but these plants old individuals. In localities in were probably several years some

Botshol Batrachospermum disappears in summer owing to the continually rising chlorinity; the tolerance to high chlorinity of Batrachospermum is considerable lower than in the case of Chaetophora. After cold winters zonation be observed. In an interesting may after the cold I found in immedi- 1956, very Fcbruary-month, Botshol, ately below the water level a 25 cm broad belt of Chaetophora germlings.

With greater depth the numbers of Chaetophora decreased, but here enormous bushes of Batrachospermum, with welldeveloped gonimoblasts occurred. In the end of May this zonation-pattern had become in- distinct of in the belt. by settling young Batrachospermum uppermost

Nevertheless in the deeper water the Batrachospermum ’s were consider- ably larger. The cause of this temporary zonation was the icc-laycr, all After of the measuring 25 cm, and killing algae by freezing. melting ice Chaetophora could develop directly, by germinating of resting stages. The invasion of followed somewhat later in the Batrachospermum season, after of the formed in the development carpospores, gonimoblasts.

Classification of the association

Westhoff (1949) supposed the algal lasion ofPhragmites and Typha- stalks to contain characteristic species for the Scirpeto-Phragmitetum or THE BATRACHOSPERMETO-CHAETOPHORETUM 253

based that Phragmition. This supposion was on the misconception, a and its mutual affection occurs between Scirpeto-Phragmitetum submerg- ed lasion. This is by no means the case. The algal vegetation in reed- borders develops only in such places, where light conditions and also

It indifferent exposition to wavedashing are favourable. is, however, absent to the kind of substrate, which only serves for attachment. It is from thin reed- and Typha beds, which are exposed to wave-action. The combination of Batrachospermeto-Chaetophoretum and Scirpeto-

Phragmitetum, although often found, has to be considered as an oc- casional one.

The Batrachospermeto-Chaetophoretum must be classified as a part of

the freshwater-series of the 1Cladophora- formation, by reason ofits physio- its life-form and its stratification. gnomy, pattern

Succession and competition

Observations on succession and competition have been made in

Botshol and Naardermeer from 1953 to 1957. The Batrachospermeto-

Chaetophoretum only has been met with on reed- and Typha stalks more old. On stalks than a young no algal vegetation occurs, owing to ydar " the of the reed. On shoots of rapid growth young only species Hydra

have been found, in Botshol mainly Hydra vulgaris f. attenuata Pall., in dominant other ponds Pelmatohydra oligactis Pall, may be the species, When the of while also other Hydra ’s may occur. growth the reed

declines and comes to a stand-still, settlement of other species takes

place. What species will establish themselves depends mainly on the of and the wave-action. At the end of quantities light on exposure to

the summer and in autumn settlement of Cordylophora caspia, Euspongilla

lacustris and a number of algae viz. Nostoc sphaericum, Phormidium tenue, small Oedogonium sp., Spirogyra sp., and the hemisphaerical form of incrassata settles Chaetophora may be observed. Batrachospermum rarely first In sheltered localities the favoured in the year. algae are highly the by the scanty movement of water. They crowd out nearly all

, which are driven back to the deepest parts of the reedstalks.

The limit between the Batrachospermeto-Chaetophoretum and the zoocoe-

nose below it, is determined by mutual competition.

stations However, the colonies prefer more exposed to water-

movement, and here the algae stand little chance of settling. Only

Cladophora glomerata competes succesfully with the animals and occupies

the belt of 0-15 (25) cm below the water level. The remaining parts of

the stalks are densely covered by Cordylophora caspia and Dreissena the also the lacustris polymorpha, on deepest parts by sponges Euspongilla and Ephydatia fluviatilis. The inconspicuous Hydra-species remain

common. In exposed stations in the lakes and ponds of Friesland and the north-western of the zonation but here part Overijsel same occurs, the Bryozoon Plumatella fungosa (Pall.) is often dominant. Animals have been observed in small feeding on algae very quantities in the Batrachospermeto-Chaetophoretum. Their influence is negligible.

Only the following snails were found: Planorbis planorbis (L.), Acroloxus 2. Sheltered and in the Fig. locality with Phragmites- Typha-growth northern part

of Botshol; a typical station of the Batrachospermelo-Chaetophoretum.

Fig. 3. Stand of Typha latifolia, exposed to wave-action along the Grote Wije, Botshol. The submerged lasion of this vegetation is characterized by the hydroid Cordylophora caspia. To the right Cladium mariscus is visible. THE BATRACHOSPERMETO-CHAETOPHORETUM 255

lacustris (L.), Bythinia tentaculata (L.), Limnaea palustris (Mull.) and fluviatilis (L.).

Other animals observed in this association arc the leeches Theromyzon

tessulatum (O. F. Mull.) and Piscicola geometra (L.). The first species is a parasite of waterbirds. In Botshol it is observed only rarely outside

the Batrachospermeto-Chaetophoretum. In the Naardermeer, where ex- the tensive parts of the watersurface are covered by leaves of Nymphaea reedborders. alba it is confined to them, and was never observed in the ,

Piscicola geometra, a parasite of fishes, occurs only in the outermost part

of the reedborder, in sheltered as well as in exposed stations.

Distribution

The association is widely distributed in the lakes and ponds of the in western part of the Netherlands. I ascertained its occurrence the Botshol, the Naardermeer, the broads of Loosdrecht (Loenerveense Plas, Eerste Loosdrechtsc Plas), the broads of Nieuwkoop, ditches in data the Alblasserwaard, near Kudelstaart and near Nigtevegt. No available from lakes of of the are the the north-western part province of Overijsel. In the turbid lakes of the province of Friesland I did not

succeed in finding the association but Mr. A. S. Tulp kindly send me a

fine sample of Batrachospermum moniliforme, collected on reedstalks in

the Groote Widen near Leeuwarden.

in Except in the lacustrine district the association occurs dunepools

and (Rietput Tweede Korfwatertje near Petten, Quakjeswater). doubt No the Batrachospermeto-Chaetophoretum occurs in other parts of . Krok (1869, cited by Luther, 1953) mentions Chaetophora incrassata, together with Batrachospermum moniliforme and Draparnaldia

glomerata (= D. plumosa) from the Bothnian Gulf near Haparanda,

where the salinity amounts to ca. 1 NaCl. Margalef (1953) found °/ 00 the association of Batrachospermum moniliforme and Chaetophora incrassata

in a small, slowly running stream with Potamogeton, Callitriche, Nasturtium and in the north-eastern of the Balearic island a grass, part Majorca. Besides the characteristic species he found also Draparnaldia plumosa,

Spirogyra sp., Tolypothrix distorta, much diatoms and a few desmids,

which findings enlarge the agreement with the Dutch vegetation.

However, the mass-occurrence of Cladophora fracta rivularis and the

mosses Platyhypnidium rusciforme and Fontinalis durieui points to the Oxyrrhynchietum rusciformis, the moss-dominated association of eutrophic

in running water. Thus slowly running water both associations can

occur mixed. Kann informed Dr E. kindly me, that she observed Batrachospermum moniliforme together with Chaetophora cornu-damae ( = Ch. incrassata) in the Traunsee in Austria. Some vegetations described by Waern (1939) from the Swedish lake Takern and by Kann (1958) from lakes in

Holstein show a close floristic relation with the Batrachospermeto-

but Chaetophoretum, are not identical. 256 C. DEN HARTOG

SUMMARY

The is characteristic Batrachospermeto-Chaetophoretum a very algal association, widely distributed in oligohalinous as well as in eutrophic and mesotrophic fresh- water in the lakes and ponds in the western part of the Netherlands. It prefers

and occurs shaded stations, sheltered from wave-action on reeds, Typha stalks and but also stones and live snails. The association be found the waterplaats, on may whole year round; Batrachospermum moniliforme is a perennial species, propagating in spring, Chaetophora incrassata an annual one.Owing to its small light requirement the association is bordered the limit the at upper by photophilous Cladophoretum glomeratae lacustre; the lower limit is determined by competition with sessile animal colonies. the association has wide distribution in Probably a Europe.

ACKNOWLEDGEMENTS

identified I am much indebted to Dr. J. Th. Koster (Leyden), who some Cyano- phyceae from the samples, and to Dr. P. Bourreily (Paris), Dr. T. Christensen(Copen- hagen), Dr. E. Kann (Vienna), Dr. H. Luther (Helsinki) and Dr. R. Margalef the distribution (Barcelona) for personal communications on of the association. Further I the direction of the Behoud wish to express my gratitude to “Verenigingtot

for the van Natuurmonumenten” permission to carry out my investigations in its domains,and to Mr. R. J. de Wit (Amsterdam) for assistence in obtaining permission

to study the algal vegetation of Botshol in the breeding season. Dr. K. F. Vaas (Leyden) kindly corrected the English text.

REFERENCES

Hartog, C. den. 1958. Epilithische algengemeenschappenin Nederland. Handel. Hydrobiol. Ver. 10: 6-8.

Hubschmann, A. von. 1953. Einige hygro- und hydrophile Moosgesellschaften Norddeutschlands. Mitt. Flor-soz. Arbeitsgem. 4: 15-25. Israelsson, G. 1942. The freshwater Florideae of Sweden. Symb. Bot. Upsal. 6,1: 1-134. Kann, E. 1958. Der Algenaufwuchs in der eulitoralen Zone alpiner und nord- deutscher Seen. Verb, intern. Ver. Limnol. 13: 311-319.

Krok, Th. O. B. N. 1869. Bidrag till kannedomen om Alg-floran i inre Ostersjon och Bottniska viken. Ofvers. K. Vet.-akad. Forh. 26: 67-92. 1953. Luther, H. Uber die Nordische Verbreitung von Chaetophora incrassata (Huds.) Hazen. Bot. Not.: 317-340.

R. 1953. la de Margalef, Materiales para la hidrobiologia de isla Mallorca. Publ. Inst. Biol. Aplic. 15: 5-111.

Symoens, J- J- 1957. Les eaux douces de 1’Ardenne et des regions voisines: Les milieux et leur vegetation algale. Bull. Soc. Roy. Bot. Belg. 89: 111-314. in Rietz Waern, M. 1939. Epilithische Algenvegetation, G. E. du a.o. Zur Kenntnis der Vegetation des Sees Takern. Act. Phytogeogr. Suec. 12: 43-50. 1952. shore in the Act. , Rocky algae Oregrund Archipelago. Phytogeogr. Suec. 30: 1-298. V. 1949. Flora de Botshol Westhoff, Landschap, en Vegetatie van nabij Abcoude.

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