Digitaria setigera
Common names
Pacific crab grass
Biostatus
Native
Category
Vascular
Structural class
Grasses
Flower colours
Brown, Purple
Detailed description
Annual, weakly caespitose to loosely matted grass forming tufts up to 1 m tall (usually much less). Stem rooting at lower nodes. Leaf-sheath folded, ribbed, light green to dark green, sometimes glaucescent or darkly maroon pigmented, bearing long, fine, spreading, tubercle-based hairs. Ligule 1.0‒2.5 mm, membranous, glabrous, truncate, erose. Leaf-blade 35‒100 × 2‒7 mm, light green, dark green, often glaucescent, soft, linear tapering to long, finely pointed tip, surfaces finely hairy, ribs and margins scabrid. Culm 0.1‒0.45(‒1.0) m, ascending-erect or floppy, internodes glabrous. Raceme 3‒5, 35‒100 mm, slender, compressed, digitate or spreading; rachis 3-angled, winged, 0.3‒0.8 mm widfe, scabrid on angles, short-hairy at base. Spikelets 2.5‒3.5 mm, paired, lanceolate, long-acute, laterally with fine acute-tipped hairs. Lower glume 0, or reduced to a minute rim or scale c.0.1 mm, upper 0.6‒1.5 mm, c.¼‒(⅓) length of spikelet, 0‒3-nerved, deltoid, obtuse to subacute, glabrous, or with long hairs on margins overtopping glume. Lower floret; lemma = spikelet, 5‒7-nerved, nerves inaequidistant, glabrous, outer internerves with long hairs. Upper floret; lemma ≈ spikelet, glabrous, acuminate, yellowish or light brown (amber) at maturity; palea ≈ lemma, similar in texture and shape; anthers 1.0‒1.3 mm; stigmas brown; cayopsis c.1.5 mm, oblong.
Distribution
Indigenous. Northern Kermadec Islands where locally common on The Meyers, Herald Islets, Chanters and Napier. Recorded from Raoul Island but not confirmed from there recently. Collected once sometime between 1838 and 1840 (possibly as a genuinely naturalised occurrence) from the Bay of Islands, North Island, New Zealand. Widespread through tropical Asia, Pacific to French Polynesia and North Australia.
Habitat
Seemingly restricted to makatea and low shrubland overlying basalt tuff and rock on the smaller islands of the northern Kermadec group. Often found around the nests of Kermadec petrel (Pterodroma neglecta) and Tasman booby ( Sula dactylatra tasmani). Digitaria setigera has also been reported from Raoul Island but there it has been much confused with the superficially similar D. ciliaris (common on Raoul as an introduced species) and it is not clear if it still present on that island.
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 | At Risk – Naturally Uncommon | Qualifiers: SO
Threats
Digitaria setigera is locally common on the outer islands of the Northern Kermadec Islands group. Beyond the small area of occupancy there are no active threats known from this species, though it may have been lost from Raoul Island. Digitaria setigera is a common, and at times weedy species of the wider Pacific which is close to its world southern limit on the Kermadec Islands.
Detailed taxonomy
Family
Endemic taxon
No
Endemic genus
No
Endemic family
No
Ecology
Flowering
On the Kermadec Islands flowering may occur throughout the year.
Fruiting
On the Kermadec Islands fruiting may occur throughout the year.
Life cycle and dispersal
Annual. Seeds dispersed by sea birds, gravity and water.
Propagation technique
Not known to be cultivated in New Zealand.
Other information
Notes on status
Digitaria setigera was initially treated as indigenous to the Kermadec Islands by Cheeseman (1888, 1906, 1925) and Oliver (1910). It was Sykes (1977, p. 166–167) as D. pruriens (Trin.) Büse who first treated this grass as naturalised, though his comments about it being suited to long distance avian dispersal, its close association on the Kermadec Islands with sea bird nesting sites and other general comments about its indigenous status in the ‘Tropical Pacific’ implies that he may also have considered it indigenous there. Velkamp (1973), who synonymised D. pruriens with D. setigera, included the Kermadec Islands in this species’ natural distribution without further comment. Despite this, Edgar & Shand (1987), Edgar & Connor (2000, 2010) treated Digitaria setigera as naturalised to the Kermadec Islands though without providing any justification for their decision (it is assumed they took advice from W.R. Sykes). Despite this view, Pacific flora and grass treatments and view points of botanists studying that region, notably including Sykes himself when questioned in 2013, regard this grass as indigenous to tropical Asia, Malesia, the Pacific Islands and northern Australia, and significantly with respect to the Kermadec Islands, also the nearby Norfolk Island group, so its presence on the Northern Kermadec Island group is not incompatible with it being indigenous there (Green 1994, Whistler 1995; Edgar & Connor 2010; R. O. Gardner, W.R. Sykes & W.A. Whistler pers. comm. December 2013). For this reason de Lange et al. (2018) accept Digitaria setigera as indigenous to the Kermadec Islands. The sole New Zealand record noted by Edgar & Connor (2000, 2010) is however, probably a genuine naturalisation stemming from early shipping.
Manaaki Whenua Online Interactive Key
NVS code
The National Vegetation Survey (NVS) Databank is a physical archive and electronic databank containing records of over 94,000 vegetation survey plots - including data from over 19,000 permanent plots. NVS maintains a standard set of species code abbreviations that correspond to standard scientific plant names from the Ngä Tipu o Aotearoa - New Zealand Plants database.
DIGSET
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 | At Risk – Naturally Uncommon | Qualifiers: SO
2012 | At Risk – Naturally Uncommon | Qualifiers: OL, SO
2009 | Not Evaluated
2004 | Not Evaluated
Referencing and citations
References and further reading
Cheeseman TF. 1888. On the flora of the Kermadec Islands: with notes on the fauna. Transactions and Proceeding of the New Zealand Institute 20: 151–181.
Cheeseman TF. 1906. Manual of the New Zealand Flora. Government Printer, Wellington,
Cheeseman TF. 1925. Manual of the New Zealand Flora. 2nd ed. Government Printer, Wellington.
de Lange PJ, Rolfe JR, Barkla JW, Courtney SP, Champion PD, Perrie LR, Beadel SM, Ford KA, Breitwieser I, Schönberger I, Hindmarsh-Walls R, Heenan PB, Ladley K. 2018. Conservation status of New Zealand indigenous vascular plants. 2017. New Zealand Threat Classification Series, 22: 1–82.
Edgar E, Connor HE. 2000. Flora of New Zealand. Vol. V. Grasses. Christchurch, Manaaki Whenua Press. 650 p.
Edgar E, Connor HE. 2010. Flora of New Zealand. Vol. V. Grasses, 2nd edition. Christchurch, Manaaki Whenua Press. 650 p.
Edgar E, Shand JE. 1987. Checklist of Panicoid grasses naturalised in New Zealand; with a key to native and naturalised genera and species. New Zealand Journal of Botany 25: 343–353.
Oliver WRB. 1910. The vegetation of the Kermadec Islands. Transactions and Proceedings of the New Zealand Institute 42: 118–175.
Sykes WR. 1977. Kermadec Islands Flora. An annotated checklist. With Appendix: Hepaticopsida (Hepaticae) & Anthocerotopsida by Ella O. Campbell. New Zealand Department of Scientific and Industrial Research Bulletin 219: 1–199.
Veldkamp JF. 1973. A revision of Digitaria Haller (Gramineae) in Malesia. Blumea 21: 1–80.
Whistler WA. 1995. Wayside Plants of the Islands – a guide to the lowland Flora of the Pacific Islands. Ilse Botanica, Honolulu, Hawaii.
Attribution
Prepared by P.J. de Lange for NZPCN, 29 May 2020. Description adapted from Edgar & Connor (2000).
Some of this factsheet information is derived from Flora of New Zealand Online and is used under a Creative Commons Attribution 3.0 New Zealand licence.
NZPCN Fact Sheet citation
Please cite as: de Lange, P.J. (Year at time of access): Digitaria setigera Fact Sheet (content continuously updated). New Zealand Plant Conservation Network. https://www.nzpcn.org.nz/flora/species/digitaria-setigera/ (Date website was queried)