Nitella C.Agardh

Casanova, Michelle T. & Karol, Kenneth G., 2023, Charophytes of Australia’s Northern Territory - II. Tribe Nitelleae, Australian Systematic Botany 36 (4), pp. 322-353 : 324

Nitella C.Agardh , Syst. Alg. xxvii (1824)

Monoecious or dioecious. Plant axis and branchlets ecorticate. Stipulodes absent; branchlets in 1 whorl, or more than 1 whorl, per node, ecorticate; primary segments usually distinctly forked into 2–8 secondary segments, or further furcate. Terminal end segments (dactyls) 1–8 cells long. Gametangia arranged at the branchlet nodes, rarely at the axial nodes; antheridia terminal and oosporangia lateral. Helical cells of the oosporangium terminated by a coronula of 10 cells, in 2 rows of 5. Oospores usually flattened spheres or ovals, with 1–3 basal-cell impressions.

Type: Nitella opaca (C.Agardh ex Bruzelius) C.Agardh.

Key to the species of Nitella in the Northern Territory

Oospores are a reliable morphological means of identifying species of Nitella . A comparison of specimen oospores with the pictures provided in the illustrations can provide definitive identification. In the absence of oospores (or a microscope), the following key can assist in distinguishing among species. A good-quality hand-lens is necessary to see features of the dactyls and whorls in most species.

1. Plants monoecious…......................................................................2

Plants dioecious…..........................................................................5

2. Branchlets once-furcate; dactyls consisting of a single cell….......... ................................................................................... N. belangeri

Branchlets 2 or 3× furcate; dactyls consisting of 2 cells…...........3

3. Axes narrow, 0.4–0.5 mm in diameter; plants less than 15 cm high; dactyls long….............................................................................4

Axes ~ 1 mm in diameter; plants up to 25 cm high; dactyls very short (brachydactylous)…......................................... N. tumulosa

4. Plants unevenly 2(–3)× furcate; sterile branchlets ~ 5 mm long; end-cells long-conical….......................................... N. townsendii

Plants evenly 3(–4)× furcate; sterile branchlets up to ~ 10 mm long; end-cells shortly conical…..................... N. boreali-australis

5. Branchlets in a single whorl of 6–8 at a node…...........................8

Branchlets in more than 1 whorl, with more than 10 (up to ~40) branchlets arising at the nodes…...............................................6

6. Branchlets in 2 whorls, up to ~ 10 in the shorter (secondary) whorl….......................................................................................7

Branchlets in 3 whorls, or so many branchlets as to be difficult to count…....................................................................... N. congesta

7. Plants up to 10 cm high; branchlets up to 5 mm long; primary branchlet whorl 1–2× furcate…................................. N. biformis

Plants up to 40 cm high; branchlets up to 10 mm long; primary branchlet whorl 2–3× furcate….......................... N. heterophylla

8. Branchlets 2 or 3× furcate; end-cells conical and acute…..........10

Branchlets 3 or more× furcate; end-cells long and obtuse…........9

9. Branchlet segments at all fucations 4–7; fertile whorls dispersed, with long primary segments…...................................... N. limosa

Branchlet segments at all furcations 2–5; fertile whorls compact, with short primary segments…............................. N. myriotricha

10. Plants less than 10 cm high; in arid- and semi-arid-zone waters…......11 Plants greater than 10 cm high; in wet–dry tropics….................12

11. Dactyls notably wider than the branchlet segments (inflated), tapering towards the end-cell…................................... N. micklei

Dactyls similar to branchlet segments; end-cell an obtuse bristle on the branchlet tips…............................................ N. acanthospora

12. Primary branchlet segment>60% of branchlet length (the remaining segments make up little brushes on the tips) …................13

Primary branchlet segment up to 50% of the total branchlet length…....................................................................................15

13. Plants with mucus; 6 branchlets in a whorl…........... N. crocodylus

Plants without mucus; 6–8 branchlets in a whorl…....................14

14. Branchlets without a central (percurrent) secondary segment…...... ........................................................................................ N. nitida

Branchlets with a central (percurrent) secondary segment….......... ................................................................................ N. oollooensis

15. Axes wiry and tangled, gametangia at the branchlet tips…............ ..................................................................................... N. martinii

Axes soft and flabellate….................................................. N. silicea