Isoetes heldreichii

Isoetes heldreichii is known only from its type locality at Palaiokastro, near the modern city of Karditsa in central Greece.^[3][4] The original habitat was a cluster of perennial springs at the foot of Mount Pindus, where Haussknecht collected submerged plants in July 1885. Those springs were later diverted to supply drinking water to Karditsa, and the pool in which the quillwort grew has disappeared. Despite targeted searches, no further populations have been located, and the species is therefore regarded as extinct in the wild.^[5]

Isoetes heldreichii was first described in 1886 by the Austrian botanist Richard von Wettstein,^[6] who based the name on material collected the previous summer in Thessaly by Carl Haussknecht.^[7] Wettstein incorrectly assumed that his travelling companion Theodor von Heldreich had discovered the plant and therefore dedicated the epithet to him.^[5]

A re-examination of Haussknecht's original gatherings confirmed that the species is morphologicallydistinct from all other Greek quillworts. It possesses only 7–14 slender leaves per corm, each about 16–18 cm long and barely 1 mm wide, and it produces relatively large megaspores—340–570 micrometres (μm) in diameter—densely covered with tiny warts. Its microspores are 27–32 μm long and bear short spines. The smooth external cuticle of the leaves and the permanently submerged habit further separate it from the more widespread I. haussknechtii and the Mediterranean I. delilei.^[5]