Nitella hollerbachii R.E. Romanov, V.Yu. Nikulin

Nitella hollerbachii R.E. Romanov, V.Yu. Nikulin & A.A. Gontcharov, sp. nov.

Diagnosis: — Nitella hollerbachii differs from N. translucens ( Persoon 1807: 531) C. Agardh (1824: 124) by having axillary, not apical heads, a more delicate and smaller general appearance, ITS sequence. It differs from an epitype of N. axillaris A. Braun (1859: 356) from Venezuela (which has a granulate oospore with short projections, see below in discussion) by having a reticulate oospore surface. Nitella hollerbachii differs from N. axillaris auct. by having bigger heads, the usual presence of 3–furcate fertile branchlets, the presence of 5 dactyls, smaller oospores and antheridia, and more numerous meshes across oospore fossa. Nitella hollerbachii differs from (mostly) Mediterranean N. brachyteles A. Braun in Leonhardi (1864: 173) by typically having very shortened dactyls which are nearly invisible to the naked eye. There is no published reliable description of ripe oospores for N. brachyteles . Nitella hollerbachii differs from New World N. caroliniana (Imahori & R.D. Wood in R.D. Wood 1962: 22) R.E. Romanov (2025a: 1) by having more numerous sterile dactyls (3–4 vs. 1–2), strictly 2–celled dactyls, and absence of bifid end cells of dactyls. Nitella hollerbachii differs from N. leptoclada A. Braun (1868: 880) by having well-developed heads and absence of mucilage. Nitella leptoclada is a species with unknown oospore surface, because ripe oospores are missing in the type specimen (LISU) that was checked by R.D. Wood and R.E. Romanov. Nitella hollerbachii differs from N. sublucens T.F. Allen (1895: 70) by having clustered oogonia at branchlet nodes only and an absence of gametangia at bases of branchlet whorls. Nitella sublucens appears to be most similar to N. hollerbachii , but it has solitary oogonia at branchlet nodes and clustered oogonia at bases of branchlet whorls. Nitella hollerbachii differs from East-Asian N. axilliformis Imahori (1951: 215) by having clustered oogonia, an absence of gametangia at the bases of branchlet whorls, the common presence of 3–furcate fertile branchlets, well-developed, larger fertile heads, smaller oogonia (250–375 vs. 400–430 μm long) and antheridia (168–185 vs. 180–210 μm in diameter). Nitella axilliformis has a similar appearance to N. hollerbachii , similar oospore traits and the same rare occurrence of 2–furcate branchlets without short secondary rays in comparison to dactyls. Nitella hollerbachii differs from New World N. praelonga A. Braun in A. Braun & Nordstedt (1883: 40) and N. cernua A. Braun (1859: 354) by having bicellular dactyls and a lack of mucilage. Nitella hollerbachii differs from Malagasy N. heteroteles that has a similar ITS by having shortened, strictly bicellular, dactyls, a sharp difference in structure between sterile and fertile branchlets, much longer primary rays of sterile branchlets, shortened fertile branchlets in heads at lateral branches, and smaller antheridia. Nitella hollerbachii differs from East-Asian N. moriokae R.D. Wood (1952: 335) and N. spiciformis Morioka (1941: 63) that have similar ITS, by having shortened, strictly bicellulate, dactyls, a different structure of the sterile and fertile branchlets, reticulate oospore surface, and shortened fertile branchlets in heads at lateral branches only. Nitella hollerbachii differs from N. moriokae by having smaller oogonia, oospores, and antheridia. Nitella hollerbachii differs from South American N. arechavaletae Spegazzini (1883: 224) and New Zealand N. tricellularis ( Nordstedt 1880: 15) Nordstedt in T.F. Allen (1888: 40 a) and N. setchellii (R.D. Wood 1962: 22) R.E. Romanov (2025a: 2) by having 2–celled, rather than 3–celled dactyls. Nitella hollerbachii differs from South African dioecious N. conifera Groves & Stephens (1933: 273) , N. dregeana A. Braun ex Kützing (1849: 517), N. euarthra (A. Braun 1868: 878) Compère (1982: 280), N. grandis A. Braun ex Kützing (1857: pl. 37), N. macilenta (A. Braun 1868: 878) R.E. Romanov (2025a: 2), and N. praeclara Groves & Stephens (1926: 148) by being monoecious. The differences listed above are summarized in the following key.

Key for the identification of Nitella hollerbachii

1. Dioecious........................................................... N. conifera , N. dregeana , N. euarthra , N. grandis , N. macilenta , and N. praeclara

- Monoecious ........................................................................................................................................................................................2

2. (2–)3–, 3–, 3–4–celled dactyls............................................................................. N. arechavaletae , N. setchellii , and N. tricellularis

- 1– or 2–celled dactyls.........................................................................................................................................................................3

3. 1–celled dactyls; heads embedded in mucilage....................................................................................... N. cernua and N. praelonga

- 2–celled dactyls; without mucilage ....................................................................................................................................................4

4. Heads very small, axillary .............................................................................................................................................. N. leptoclada

- Heads evident, axillary or apical, or uppermost whorls of branchlets small and uniformly distributed along axis resulting in loosely spicate appearance, or ends of young axes give impression of small heads ......................................................................................5

5. Dactyls short, but easily recognizable to the naked eye................................................................................................ N. brachyteles

- Dactyls very short, invisible to the naked eye....................................................................................................................................6

6. Oospore surface granulate, papillate or tuberculate ...................................................... N. axillaris , N. moriokae , and N. spiciformis

- Oospore surface reticulate ..................................................................................................................................................................7

7. Heads apical................................................................................................................................................................... N. translucens

- Heads axillary.....................................................................................................................................................................................8

8. 1–2 dactyls in sterile branchlets; 2–3–celled dactyls; end cells of dactyls occasionally bifid ..................................... N. caroliniana

- 1–4 dactyls in sterile branchlets; strictly 2–celled dactyls; end cells of dactyls not bifid..................................................................9

9. Gametangia both at bases of branchlets and branchlet nodes .......................................................... N. axilliformis and N. sublucens

- Gametangia at branchlet nodes only............................................................................................................................ N. hollerbachii

Description ( Figs 1–20 View FIGURES 1–2 View FIGURES 3–14 View FIGURES 15–20 ): —Monoecious plants are fresh green, slender, medium-sized, without lime incrustation, at least 10 cm high, and without mucilage ( Figs 1, 2 View FIGURES 1–2 ). The stems are rather thin, 400–625 μm diameter, flexible, and richly branched especially at the plant base. The internodes are neither shortened nor elongated, more or less equal to each other at the whole stem, 13–25 mm long, equal to branchlet length, or slightly longer or shorter than the branchlets. Whorls of sterile and fertile branchlets are sharply dimorphic. The sterile whorls consist of 5–6 long, slightly curved, 1– or sometimes 1–2–furcate branchlets, creating a narrow cone in outline. Primary rays of sterile branchlets are long, 10–20 mm long, 220–440 μm in diameter. Dactyls or, in other words, secondary rays of sterile branchlets are greatly condensed, very short, hardly recognizable under hand lens, 3–4, 2–celled, in the shape of spines, forming an end corona. The penultimate cells of dactyls are larger and wider; end cells are sharp-pointed and conical. Sometimes penultimate cells of one or two dactyls are greatly elongated. In this case, this penultimate cell is tipped with ordinary solitary conical end cells or forked into 3–4 small dactyls (tertiary rays) making the branchlet 1–2–furcate. An elongated penultimate cell below a single spine-shaped end-cell is rare. The 3–5 fertile branchlet whorls are formed at 2–5 greatly condensed lateral branches inside the base of whorls of sterile branchlets. The lateral branches have elongated ovoid outlines because of the dense placement of shortened branchlets that are clasped together in dense heads 1.3–3.4 mm in diameter inside the base of whorls of sterile branchlets. The well-developed lateral branches are 1.7–3.1 mm long and 1.2–1.8 mm wide. The heads formed within them are lobate in the pressed state reaching up to 5–5.6 mm in spawn. Each fertile whorl consists of 5–6 very short branchlets less than 1 mm long and 125–150 μm wide. The fertile branchlets are 1–, 2– or 3–furcate, mostly 2– or 3–furcate. There are 3–5 secondary, tertiary, and quaternary rays of fertile branchlets, more or less equal to each other, usually subsequently slightly shortening towards the apex. The dactyls of fertile branchlets are comparatively long, 2–celled, having the same arrangement as dactyls of sterile branchlets. The gametangia are conjoined, but they appear usually sejoined probably because of their uneven ripening, at branchlet furcation only. Gametangia are missing at third furcations of 3–furcate branchlets. The oogonia are rarely solitary, usually in clusters of 2–3, spherical, ovate, or slightly shortened when unripe, widely oval in ripe stage, 250–375 μm long excl. coronula, 250–345 μm wide. The spiral cells form 8–9 helical strips, not inflated at apical parts. The coronula is persistent, the cells are appressed, 33–60 μm long, 42–67 μm wide, having cells more or less equal to each other in both rows. The oospores are oval, light yellowish-brown in reflecting and transmitting light, 235–280 μm long, 188–252 μm wide, with 6–7 slightly prominent, but clear striae with very delicate, narrow, and unequally developed, flanges, easily lost during preparation for light microscopy, which hamper the view of oospore surface in scanning electron microscopy. The fossae are 39–52 μm wide. The oospore membrane is light yellow-brown, reticulate in light microscopy, with rather large uneven meshes, 10–12 meshes across the fossa. It looks somewhat imperfectly reticulate in scanning electron microscopy, especially at higher magnification and in tangential view, because of the concave mesh edges, the projected appearance of mesh vertices, and shallow pits inside meshes. Mesh size measured as the distance between most remote mesh vertices of the same mesh is 3.8–4.9 μm. The ribs are smooth to reticulate in scanning electron microscopy. The antheridia are rare, always solitary, 168–185 μm in diameter.

Holotype: — RUSSIAN FEDERATION. Primorsky Krai: Far-Eastern Territory of the USSR, Vladivostok District, rice fields at Santakheza [now Spasovka] River , 4 versts [= 4.3 km] from Lake Khanka [literal translation of the label in handwritten Russian], 17 August 1928, Vazinger-Alektorova, det. Romanov ( LE A0007562 ) ( Fig. 1 View FIGURES 1–2 ).

Isotype: — LE A 0007561 ( Fig. 2 View FIGURES 1–2 ).

Representative DNA sequences for LE: — rbc L gene ( PV 067677), ITS region ( PV 068215).

Etymology: —This species is named in honor of Maximilian Maximilianovich Hollerbach (1907–1989), a prominent Soviet charophytologist who studied the original material and prepared excellent illustrations of its morphological characters ( Hollerbach 1946, Hollerbach & Krassavina 1983).

Distribution: — Nitella hollerbachii is currently known from one locality in Pacific Asia.

Habitat: — Nitella hollerbachii thrives in rice fields. This suggests that this is an annual species relying on sexual reproduction with oospores.