Gackstroemia, Trevisan, 1877

Engel, John J., 2013, Austral Hepaticae 50. Gackstroemia in New Zealand, together with an interesting new species, Phytotaxa 118 (1), pp. 9-21 : 10

Key to species of Gackstroemia in Australasia

1. Plants (2)3-pinnate, robust, (12) 18–25 mm wide (at widest point between opposing primary branch tips); dorsal margin of main shoot leaves narrowly and sharply reflexed; ultimate branches with first branch underleaf with lobes mostly explanate, the lower lobe occasionally saccate, the underleaf lobes of ultimate branches uniformly explanate; leaf cells with the intervening walls between trigones at least moderately thickened, often strongly notably so, the lumina typically evenly rounded; stylus of main shoot leaves flat, the margins plane or weakly reflexed, often sparingly to copiously ciliate; underleaves of main shoot distinctly auriculate at the base, the lobes terminating in a single cell or a uniseriate row of 2(3) cells, that are isodiametric or at most 2X longer than wide; androecia with lobe apices rarely with a short awn; spores 85-96 µm, the wall distally with numerous close, coarse, rather high tuberculae; elaters 3-spiral, the wider 3–4-spiral, the spirals very narrow, 2 µm wide; capsule wall 4–6-stratose........ ........................................................................................................................................................ G. novae-zelandiae

1. Plants 1–2(3)-pinnate, with 3º branches lacking or at most sparingly developed, the plants small to medium in size, less than 18 mm wide (at widest point between opposing primary branch tips); dorsal margin of main shoot leaves plane, not reflexed; ultimate branches with first branch underleaf with lobes typically uniformly saccate (in some populations the upper lobe at times explanate), the underleaf lobes of ultimate branches uniformly saccate; leaf cells with intervening walls between trigones thin, the lumina irregularly sinuate, not evenly rounded; stylus of main shoot leaves cucullate, the margins distinctly reflexed, usually entire; underleaves of main shoot narrowed and angled to base, with tissue adjacent to apex and base of U-shaped insertion line forming an inverted triangle, the base never cordate or auriculate, the lobes terminating in a uniseriate row of (2)3–5 elongated cells (exc. sometimes in small phases of G. alpina ); androecia (known only in G. weindorferi ) with lobe apices each with a conspicuous awn; spores (known only in G. weindorferi ) 47-58 µm, the wall interruptedly, finely and irregularly reticulateareolate distally; elaters (known only in G. weindorferi ) 1- or 2-spiral, at times locally 3-spiral in median sector, the spirals broad, to 4.3 µm wide; capsule wall 3–4-stratose ............................................................................................. 2

2. Plants medium in size, 9–17 mm wide (at widest point between opposing primary branch tips); lobule of main shoot leaves nearly always explanate, rarely and locally transformed into a well-developed water sac; dorsal lobe of main shoot leaves with curvature at apex interrupted by a narrowly acute to abruptly and prominently apiculate process; primary branch underleaves with lobes explanate, or, at times saccate in distal half or less of branch; plants at maturity with principal axis ascending or the entire plant erect; plants rust-colored to copper-red, at most sometimes weakly tinged with magenta but not consistently so .............................................................................. G. weindorferi

2. Plants small in size, 6–11 mm wide (at widest point between opposing primary branch tips); lobule of main shoot leaves normally saccate, rare and isolated explanate ones aside; dorsal lobe of main shoot leaves with apex typically narrowly to broadly rounded, the curvature continuous and not interrupted by an angulation at the summit, with or without a cusp-like tooth (the tooth at times reduced to an angular crenate projection); primary branch underleaves often with all or most lobes saccate; plants creeping, often closely so; plants deep red to magenta or piceous ........... ......................................................................................................................................................................... G. alpina