Rytidosperma horrens
Biostatus
Native – Endemic taxon
Current conservation status
The conservation status of all known New Zealand vascular plant taxa at the rank of species and below were reassessed in 2022-2023 using the New Zealand Threat Classification System (NZTCS) – more information about this can be found on the NZTCS website. This report includes replaces all previous NZTCS lists for vascular plants. Previous assessments can be found here.
- Conservation status of vascular plants in Aotearoa New Zealand, 2023. 2024. Peter J. de Lange, Jane Gosden, Shannel P. Courtney, Alexander J. Fergus, John W. Barkla, Sarah M. Beadel, Paul D. Champion, Rowan Hindmarsh-Walls, Troy Makan and Pascale Michel Department of Conservation. Source: NZTCS and licensed by DOC for reuse under the Creative Commons Attribution 4.0 International licence.
2023 | Threatened – Nationally Critical | Qualifiers: DPT, RR
Category
Vascular
Structural class
Grasses
Flower colours
Yellow
Detailed description
Diminutive, tufted, bright green tussock with persistent, stramineous leaves below shoots of 3–4 conspicuously divergent leaf blades. Branching intravaginal. Leaf-sheath 10–15 mm, glabrous, ridged, becoming stramineous; collar thickened, paler beneath sheath; apical tuft 0.5–1.5 mm, sparse. Ligule a very narrow row of hairs c. 0.25 mm long. Leaf-blade 25–30 × 0.5 mm, ± terete; persistent, weakly disarticulating at ligule; glabrous below except keel hairy apically; upper surface with numerous small white prickles on nerves; margin glabrous. Culm to 120 mm, internodes 40–60 mm. Inflorescence racemose of 2–5, widely spaced, solitary, overlapping spikelets on very finely toothed pedicels 2–5 mm long, rachis very finely toothed. Spikelets 6–8 mm long, 3–5 florets in each; awns exserted. Glumes equal, ¡± ovate-acute 5–6 mm, glabrous, bright green centrally, margins hyaline sometimes tinged purple below, faintly toothed above, apex finely ciliate, nerves confluent; upper 5-nerved, lower 3-nerved, upper surface with abundant small, white hairs. Lemma 2 mm, bright green, 7-nerved, nerves anastomising below sinus; upper row of hairs only in marginal tufts, 0.75 mm, ≥ sinus, 0.5 mm, not reaching upper marginal tufts, other glabrous; lemma lobes 1.5–2.5 mm, ≥ lemma, abruptly produced into 1.0-1.5 mm long awns, reflexed from twisting column 1 mm. Callus 0.25 mm, rounded, marginal hair tufts 0.4–0.5 mm, hairs 1–2 = to lodicule; nerved, cuneate and lobed. Anthers 0.7–1.0 mm, yellow, apiculate, exserted. Ovary 0.5–0.8 mm, obovoid, stipitate, stigma-style 1.20–1.75 mm, exserted. Seed 1.40–1.50 × 0.75 mm, obovate.
Similar taxa
Exact relationships to other New Zealand bristle grasses is unclear. It has many of the features of the rather obviously unrelated R. merum Connor et Edgar from which it is easily distinguished by its smaller size, and much shorter inflorescences which do not elongate. The lateral lemma lobes are 1.5–2.5 mm rather than 3–8 mm long, the central awn 1.5–2.5 mm rather than 6.5–14 mm, spaced 1 mm rather than 2.5–3.5 mm away from the twisting column.
Distribution
Endemic. New Zealand: South Island (upper Maitland Catchment, Lake Ohau).
Habitat
Subalpine (1200 m a.s.l.). Recorded from wet flushes and tarn margins where it is a sparse to locally common component of short, dense, vegetation.
Threats
Recent (2009) surveys have found Rytidosperma horrens to be locally common over a large area west of Lake Ohau. In future listings this species is likely to be regarded as Naturally Uncommon.
Detailed taxonomy
Genus
Family
Synonyms
None
Endemic taxon
Yes
Endemic genus
No
Endemic family
No
Ecology
Flowering
January
Fruiting
April
Propagation technique
Has been cultivated, and flowered and set seed in Auckland and Lincoln. A small and unremarkable grass unlikely to prove popular in cultivation.
Other information
Etymology
rytidosperma: Wrinkled seed
Manaaki Whenua Online Interactive Key
Chromosome number
2n = 24
Previous conservation statuses
The conservation status of all known New Zealand vascular plant taxa at the rank of species and below were reassessed in 2022-2023 using the New Zealand Threat Classification System (NZTCS) – more information about this can be found on the NZTCS website. This report includes replaces all previous NZTCS lists for vascular plants. Previous assessments can be found here.
- Conservation status of vascular plants in Aotearoa New Zealand, 2023. 2024. Peter J. de Lange, Jane Gosden, Shannel P. Courtney, Alexander J. Fergus, John W. Barkla, Sarah M. Beadel, Paul D. Champion, Rowan Hindmarsh-Walls, Troy Makan and Pascale Michel Department of Conservation. Source: NZTCS and licensed by DOC for reuse under the Creative Commons Attribution 4.0 International licence.
2017 | Threatened – Nationally Critical | Qualifiers: RR, St
2012 | At Risk – Naturally Uncommon | Qualifiers: DP, RR
2009 | Data Deficient
2004 | Not Threatened
Regional conservation statuses
Otago: 2025 | Regionally Threatened – Regionally Critical | Qualifiers: DPS, DPT, RR
The regional threat classification system leverages off the national assessments in the NZTCS, providing information relevant for the regional context. Otago conservation status information is sourced from the “Conservation Status of Indigenous Vascular Plants in Otago, 2025” Jarvie S et al. (2025) report.
Referencing and citations
References and further reading
Molloy BPJ, Connor HE. 2005. Species novae graminum Novae-Zelandiae III. Two diploid species of Rytidosperma (Danthonieae: Danthonioideae). New Zealand Journal of Botany 43: 721–734. https://doi.org/10.1080/0028825X.2005.9512986.
Attribution
Description modified from Molloy and Connor (2005).