Isoetes tenuissima, Boreau. Selected, 1851

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 : 291-293

Lectotypification of Isoetes tenuissima

Troia & Rouhan (2018: 999) did not designate a type for this name because, at that time, no original material could be located in P and ANG. We subsequently found a sheet with I. tenuissima specimens collected by Father Théodore Chaboisseau at Rischauveron pond (Dpt. of Haute-Vienne, France) on 2 September 1847 which is the exact date cited by Boreau in the protologue of the species ( Boreau 1851: 269−270). Other sheets, with duplicate specimens of the same gathering were found during our search at P in May 2023. Therefore, after having studied these sheets and their plants, we designate the following specimen as the lectotype:

Isoetes tenuissima Boreau in Bull. Soc. Industr. Angers 21: 269. 1851.

Lectotype (designated here):— [ FRANCE] Etang sablonneux du Richaudron [= Rischauveron ], com. d’Azat, Haute-Vienne, sur les limites de la Vienne, 2 Sept 1847, Abbé T. Chaboisseau s.n. ( P barcode P01190869 ! = 7 plants on the lower half of the sheet, https://mediaphoto.mnhn.fr/media/1707752821508imPndEQUCNoYDfDw) ( Fig. 5 ); isolectotypes: P barcodes P01282562 ! and P01282579 !).

Extract from the protologue ( Boreau 1851: 269).—“ Cette espèce a été découverte le 2 septembre 1847, par l’Abbé Chaboisseau dans l’étang du Richaudron, commune d’Azat (Haute-Vienne)… ”. [English translation: “ This species was discovered on September, 2 1847, by Father Chaboisseau in the Richaudron pond, commune of Azat (Haute-Vienne)... ”].

The sheet, originally labelled as a single gathering (barcode P 01282561), is now interpreted as including two different collections, one of which (barcode P01190869; the 7 plants on the lower half; Fig. 5 ) is selected here as lectotype. Spores ( Fig. 6 ) were removed from the second individual on the right of the specimen barcoded P01190869. Considering that no other Isoetes species was growing at Rischauveron pond and due to the uniform morphology of the plants, we conclude that all seven individuals on that specimen belong to I. tenuissima and the lectotype here designated is the whole specimen P01190869.

Note.—As far as we know, the last observation and collection of I. tenuissima at the Grand Étang du Rischauveron (Rischauveron pond) was made by Louis de Vergnes on 7 August 1921 ( Boudrie et al. 2016). At that time, it was said that the plant grew abundantly in the pond, notably on its southern banks. Despite our searches on the site several times between 1980 to 2023, the plant has not been seen again. Its disappearance is most likely due to the deterioration of the water quality.

Figures

FIGURE 5. Lectotype (the seven plants on the lower half of the sheet) of Isoetes tenuissima (P barcode P01190869).

FIGURE 6. SEM images of spores from the lectotype of Isoetes tenuissima (spores were removed from the second individual from the right in the lower part of the sheet P barcode P01190869): A. Megaspore proximal view; B. Megaspore distal view; C. Megaspore equatorial view; D. Microspore equatorial view. Megaspore scale bar = 100 µm. Microspore scale bar = 10 µm.