Isoetes lacustris Quillwort

A submerged, aquatic perennial which grows in acidic, oligotrophic waters such as mountain tarns. It produces a cluster of narrow leaves in a rosette that arises from a corm-like structure which is rooted in the sediment. The leaves have 4 hollow gas channels (lacunae) which can be seen if a cut leaf is examined with a hand lens. Leaves are 10-45cm long, up to 12mm wide and tend to stand upright in the water. It sometimes grows with Spring Quillwort (Isoetes echinospora) in shallow water near the shore but it often grows in much deeper water up to 5m in depth where it can form extensive lawns. It differs from Spring Quillwort in its stiff leaves which are not tapered for most of their length, but narrow to a blunt, assymetric point near the apex. Spores of two types are produced in sporangial sacs at the bases of the leaves. A single, large megaspore is produced in each of the outer leaves and clusters of much smaller microspores are produced in the mddle layer of leaves.The megaspores of Quillwort are covered in anastomosing ridges, unlike those of Spring Quillwort which are covered in small spines. It is a Boreal-Montane species which has a mostly western and northern distribution in upland Britain. It has decreased in parts of its northern range and has been lost from many of its lowland sites, but because of the difficulties involved in surveying benthic flora in deep water it is probably under recorded. It is uncommon in south Wales but has been known in West Glamorgan from Llyn Fach, Neath Port Talbot, for over a hundred years, where it grows with Spring Quillwort. It was also known from nearby Llyn Fawr, Rhondda Cynon Taff, in the 19th Century but has not been recorded there in recent times.

Native

See account of Spring Quillwort for details about carbon dioxide assimilation and photosynthesis in quillworts.