Lamprothamnium sardoum R.Becker, 2022

Casanova, Michelle T. & Becker, Ralf, 2022, Lamprothamnium sardoum sp. nov. (Characeae, Streptophyta): A new species of Lamprothamnium for Europe, Phytotaxa 567 (3), pp. 269-277 : 271-272

Lamprothamnium sardoum R.Becker , sp. nov. ( Figs 1–3 )

Type:— ITALY. Sardini , circa San Giovanni Sinis, in aquis stag., 39°53’13 N, 8°26’22 E, WGS 84, 05 April 2018, Becker 2018 (Herb. ROST) .

The monoecious plants are small to medium–sized (9–17 cm including the protonema), light green, opaque and not incrusted, with well developed, long stipulodes and bract-cells ( Fig. 1 B, C ). The bright orange gametangia are clustered inside and outside the base of the whorl and on the lowest branchlets ( Fig. 2B ), and are abundant and obvious, even in situ in the habitat ( Fig 2A ). Plants grow as individual shoots, fertile at nearly all nodes, with long whispy protonemal axes longer than the height of the plants ( Fig. 1B ). Axes narrow, 350–600 µm in diameter (usually 375–550 µm), ecorticate, internodes 1–3.2 cm long except in the apicies. Stipulodes, up to one per branchlet (but frequently replaced by gametangia; Fig. 1A ), up to 1.75 mm long, downward and outward pointing where present. Branchlets 5 to 8 in a whorl, up to 1.8 cm long, basal branchlet cell short on fertile branchlets, up to 2 mm long ( Fig. 1C ), sterile branchlets not seen. Branchlet end segments usually 1 cell, up to 750 µm long, mucronate ( Fig. 2D ). Bract cells verticillate (4 or 5 around) on the lowest two or three branchlet nodes in fertile whorls, up to 1.7 mm long ( Fig. 2C ). Gametangia clustered inside and outside the base of the whorl and conjoined, geminate or geminate-conjoined on the lowest 2–3 branchlet nodes ( Fig. 1A ). Oogonia bright orange ( Fig. 2B ), apparently sessile, clustered inside and outside the base of the whorl, and when occurring on the branchlets, usually conjoined with antheridia, below or beside the antheridium, 500–750 µm long, 400–600 µm wide (only dry material was measured), with 10–14 convolutions ( Fig. 1D ). Coronula 75–110 µm long, 130–150 µm wide, coronula cells oval-shaped ( Fig. 1E ). Oospores black, 510–650 µm long, 250– 475 µm wide at the widest point, with 9–11 striae of low ridges, ornamentation smooth ( Fig. 3 , Fig.2E ). Antheridia 325–450 µm in diameter, orange, solitary or conjoined with oogonia on the branchlets ( Fig. 1D ), as well as inside and outside the base of the whorl. Vegetative reproduction not known. Chromosomes not known.

Etymology: The specific epithet is named for the island of Sardinia where collection was made.

Figures

FIGURE 1. Morphology of Lamprothamnium sardoum R.Becker. A) placement and arrangement of gametangia at the base of the whorl and on the branchlets (some branchlets removed) illustrating abundant gametangia clustered and geminate on the branchlets, as well as inside and outside the base of the whorl. Scale = 0.5 mm. B) Herbarium material (circled) showing long protonemata and fox-tail whorls. Scale = 1 cm. C) Apex of plant with several whorls. Gametangia are abundantly visible on the thallus, along with verticillate, spreading bract cells. Scale = 0.5 mm. D) Arrangment of gametangia when conjoined, antheridium above oogonium in common with other species of Lamprothamnium. Scale = 0.1 mm. E) Fertilised oospore and bract cells on a branchlet.

FIGURE 2. Lamprothamnium sardoum in life. A) Sparse stands in shallow, brackish water in its habitat (Sardinia, 2018–04–05). Scale = 10 cm. B) Detail of the base of a whorl with abundant gametangia. Scale = 2 cm. C) Branchlet tips. Scale = 1 mm. D) Detail of single branchlet end cell. Scale = 0.5 mm. E) Oospore attached to the base of the plant. Scale = 200 µm (Photos R. Becker).

FIGURE 3. Oospore removed from the base of plant (the only mature oospore available on the type material). A) side view of oospore, damaged via germination. Scale = 200 µm. B) Detail of oospore wall. Scale = 10 µm.