Nostoc pruniforme

{{Short description|Species of bacterium}}

{{Speciesbox

| name = Mare's eggs

| image = CyanobacteriaColl1.jpg

| image_alt =

| image_caption =

| genus = Nostoc

| species = pruniforme

| authority = C.Agardh ex Bornet & Flahault

| synonyms =

| synonyms_ref =

}}

Nostoc pruniforme (Mare's eggs) are a species of cyanobacterium. These freshwater bacteria grow in colonies which take the form of dark green, gelatinous spheres with a smooth surface like a plum. It is common and widely distributed both geographically and ecologically in oligotrophic and mesotrophic freshwaters in temperate and sub-Arctic regions.{{Cite journal|last=Sand-Jensen|first=Kaj|date=July 2014|title=Ecophysiology of gelatinous Nostoc colonies: unprecedented slow growth and survival in resource-poor and harsh environments|journal=Annals of Botany|volume=114|issue=1|pages=17–33|doi=10.1093/aob/mcu085|issn=1095-8290|pmc=4071103|pmid=24966352}}

In temperate lakes, N. pruniforme appears to grow in diameter from ~0·2 cm in late spring to 2–3 cm in midsummer and it can rapidly die off, supposedly because of attacks by viruses or bacteria at high summer temperatures (K. Sand-Jensen, unpubl. data). In contrast, in a cold (4 °C), nutrient-poor spring in Oregon, USA, N. pruniforme reached a handball size of 15–17 cm in diameter and weighed 2.6 kg after sustained slow growth for 9–14 years.{{Cite journal|last=Dodds|first=Walter K.|last2=Castenholz|first2=Richard W.|date=September 1988|title=Effects of grazing and light on the growth of Nostoc pruniforme (Cyanobacteria)|journal=British Phycological Journal|volume=23|issue=3|pages=219–227|doi=10.1080/00071618800650251|issn=0007-1617}} Very large colonies are also found in cold transparent lakes in Greenland (K. Sand-Jensen, unpubl. data). In addition to their larger size and persistence, they differ from Danish temperate specimens by having a more solid surface and a denser gel.