Isoetes echinospora Durieu, 1861

Boudrie, Michel, Rouhan, Germinal, Malécot, Valéry & Troia, Angelo, 2024, On the typification of three Isoetes names (Isoetaceae, Lycopodiopsida) described from France, Phytotaxa 641 (4), pp. 286-294 : 289-291

Isoetes echinospora Durieu in Bull. Soc. Bot. France 8: 164. 1861.

Lectotype (designated here):— [ FRANCE: Puy-de-Dôme ] dans le lac de Guéry, août 1850, E. Cosson s.n. ( P barcode P01217445 ! (http://mediaphoto.mnhn.fr/media/1441293183178fy6FTW1HVK76 AJWV) ( Fig. 3 ), only the plant, consisting of 7 pieces, at the left bottom of the sheet; isolectotypes: P, barcode P01217446 ! (only the 3 plants at bottom of the sheet, whose megaspores have been checked; the other plant in the upper part of the sheet belongs to a different gathering, barcode P04025759 ); possible isolectotype: P barcode P01250216 ! (no spores available).

Extract from the protologue ( Durieu de Maisonneuve 1861: 164).—“ Elle croît dans quelques lacs du centre de la France et paraît s’avancer assez haut vers le nord-ouest de l’Europe.”; [page 165] “ M. J. Gay rappelle que Dillen, dans son Historia Muscorum, publié en 1741, a figuré deux formes d’Isoëtes croissant dans le Pays de Galles, dont l’une (n° 1) ressemble à la plante du lac de Guéry en Auvergne ( I. echinospora DR. ),… ”. [English translation: [page 164] It grows in some lakes in central France and seems to extend quite high towards the north-west of Europe. [page 165] Mr. J. Gay reports that Dillen, in his Historia Muscorum, published in 1741, depicted two forms of Isoetes growing in Wales, one of which (No. 1) resembles the plant of Lake Guéry in Auvergne ( I. echinospora DR. ),…].

See Greuter & Troia (2015) for previous typifications made by both Pfeiffer (1922) and Fuchs (1962) that have to be refuted. Although we have seen several herbarium sheets whose date and site of collection were compatible with the protologue, we have selected the specimen with barcode P01217445 which includes a hand-written label by Durieu, with the gathering label (by Cosson) showing both the locality “Lac de Guéry” and the date “1850” that is prior to the date of publication of the species name. This sheet includes 12 plants in good condition and with the typical characteristics of the species. To be unequivocal, we have selected as lectotype the single plant, consisting of 7 pieces, at the left bottom of the sheet ( Fig. 3 ), from which we removed and imaged spores ( Fig. 4 ).

The cited specimens were all originally identified as I. lacustris , a distinct species that also grew in the same lake ( Greuter & Troia 2015). As the possibility of mixed specimens representing the two species or their sterile hybrid Isoetes ×jermyi Brunton & Rumsey (2021: 507) cannot be ruled out, we refrain from indicating additional potential isolectotypes (e.g. the remaining 11 plants of P01217445, P01217446, and P01224375) until all corresponding spores can be imaged to confirm the identification of each individual plant.

Note.—Lake Guéry was natural, of volcanic origin, originating from the obstruction of two watercourses by a basaltic flow, about two million years ago, followed by erosion by glacial scouring. The natural lake level was raised around 1890 to form a reservoir for a hydroelectric power station downstream (Espaces naturels sensibles - Département du Puy-de-Dôme 2023), and probably this caused the Isoetes populations to disappear. Unfortunately, no Isoetes species has subsequently been observed at the Lake Guéry.

Figures

FIGURE 3. Lectotype (the individual bottom left, dissected as seven pieces and attached to a single label) of Isoetes echinospora (P barcode P01217445).

FIGURE 4. SEM images of megaspores from the lectotype of Isoetes echinospora: A. distal view; B. proximal view; C. equatorial view. Scale bar = 100 µm.