Abrodictyum caudatum
Biostatus
Native
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: DPR, DPS, DPT, SO
Category
Vascular
Structural class
Ferns
Flower colours
No flowers
Detailed description
Diminutive, epiphytic fern. Rhizome long creeping 1–1.5 mm diameter, densely clothed with spreading bristle-like dark red-brown multicellular hairs. Fronds crowded toward rhizome apex, 10–20 mm long. Stipes 3–5 mm long, bearing two faint longitudinal ridges. Frond lamina deeply 1–2(–3) pinnatifid, broadly deltoid to narrowly ovate, 8–10(–12) mm wide, membranous, ± pale green; apex erect, ultimate segments linear, 1–3 mm long, 0.3–0.4 mm wide, ± glabrous. Sori inconspicuous, immersed in the apices of basal segments of secondary pinnae, involucre funneliform, 0.2–0.5(–1.0) mm long, 0.3–0.6 mm wide at apex, narrowly winged for most of length, ± narrowly triangular, mouth lobed 4×, lobes entire, spreading; receptacle exserted.
Similar taxa
The mainland New Zealand form of Abrodictyum caudatum is superficially similar to Polyphlebium endlicherianum and P. venosum. From Polyphlebium endlicherianum it differs by its deltoid frond and by the lobed involucre of the fruiting receptacle. Further it differs by its ecology as P. endlicherianum is rarely found in this country as an epiphyte, while Abrodictyum caudatum in New Zealand, as elsewhere in the world, is strictly epiphytic. From Polyphlebium venosum, Abrodictyum caudatum differs by having a deltoid frond, and especially by the obvious lack of distinct veins within the fronds.
New Zealand plants of Abrodictyum caudatum may yet warrant formal recognition as a separate species or subspecies (B.S. Parris pers. comm.). In particular they are much smaller than this species usually is overseas, they have a less well defined creeping rhizomatous habit, and the fronds are much smaller and less divided than is usual for this species, furthermore the involucre is distinctly divided into 4 entire lobes (it is usually entire in A. caudatum). However, Abrodictyum caudatum is a highly variable species and sequences of the New Zealand plant are the same as samples of A. caudatum from Fiji so it seems best for now to place our plant there. Raoul Island Abrodictyum caudatum are different again and they would repay further study.
Distribution
Indigenous. New Zealand: Kermadec Islands (Raoul Island), North Island (Kerikeri, Auckland). Also the wider Pacific, eastern Australia (Queensland to Victoria), New Guinea, Malesia, New Caledonia, Fiji, Samoa, Tahiti and Rarotonga.
Habitat
Epiphytic on the trunks of wheki (Dicksonia squarrosa) in lowland, riparian forest.
Threats
Currently this species is known from two sites in mainland New Zealand, the Kerikeri population is present on < 10 wheki (Dicksonia squarrosa) in a small are of riparian forest. The host trees are at risk from flooding, weeds and, as they grow alongside a popular walking track, vandalism. The population has declined since it was first discovered in the late 1990s as some host trees have died. The population is being carefully monitored by the Department of Conservation. An Auckland population has recently been dicovered, here it is found on one wheki tree, growing with Hymenodon pilifer, Tmesipteris tannensis, Lepraria ulrikii and other bryophytes (Ford, 2023). Both these populations were found by chance and it is very easily overlooked it is quite likely that further populations exist elsewhere in New Zealand. On Raoul Island (Kermadec Islands group) it is known from a single site near the summit of that island.
Detailed taxonomy
Genus
Family
Synonyms
Trichomanes caudatum Brack.; Cephalomanes caudatum (brack.) Bostock; Macroglena caudata (Brack.) Copel.
Taxonomic notes
NZPCN now follows Ebihara et al. (2006) in recognising Abrodictyum as distinct from Trichomanes—although Brownsey & Perrie (2016) rejected this idea, the generic segregation was adopted by the PPG I (2016) and is now widely followed throughout the world.
Endemic taxon
No
Endemic genus
No
Endemic family
No
Ecology
Life cycle and dispersal
Fruiting material appears to be present in the New Zealand population throughout the year.
Propagation technique
Difficult—should not be removed from the wild.
Other information
Etymology
abrodictyum: From the Greek habros ‘delicate’, ‘pretty’ and diktyon ‘net’, literally “delicate net”
caudatum: With a tail
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: DP, SO
2012 | At Risk – Naturally Uncommon | Qualifiers: DP, OL, SO
2009 | Threatened – Nationally Critical
Regional conservation statuses
Auckland: 2025 | Regionally Threatened – Regionally Critical | Qualifiers: DPR, DPS, DPT, SO, NStr
The regional threat classification system leverages off the national assessments in the NZTCS, providing information relevant for the regional context. Auckland conservation status information is sourced from the “Conservation status of vascular plant species in Tāmaki Makaurau / Auckland” Simpkins E et al. (2025) report.
Referencing and citations
References and further reading
Bostock PD, Spokes TM. 1998. Hymenophyllaceae. Flora of Australia 48, Ferns Gymnosperms and allied groups: 116–148. ABRS/CSIRO Victoria, Australia.
Brownsey PJ, Perrie LR. 2016. Hymenophyllaceae. In: Breitwieser I, Heenan PB, Wilton AD. Flora of New Zealand - Ferns and Lycophytes. Fascicle 15. Manaaki Whenua Press, Lincoln, NZ. https://doi.org/10.7931/B1QP4Z.
Ebihara A, Dubuisson, J-Y, Iwatsuki K, Hennequin S, Ito M. 2006. A taxonomic revision of the Hymenophyllaceae. Blumea 51: 2–57. https://doi.org/10.3767/000651906X622210.
Ford M. 2023. Under our nose, a second record of the bristle fern Abrodictyum caudatum for mainland New Zealand. Trilepidea 231: 3–5.
PPG 1: The Pteridophyte Phylogeny Group 2016. A community-derived classification for extant lycophytes and ferns. Journal of Systematics and Evolution 54: 563–603. https://doi.org/10.1111/jse.12229.
Attribution
Fact sheet prepared for NZPCN by P.J. de Lange 10 March 2011 with modification to threats made by M. Ford (4/12/23). Description modified from Bostock & Spokes (1998) using measurements taken from the limited New Zealand herbarium material available. Notes on variability of A. caudatum in New Zealand from B.S. Parris (pers. comm.)
NZPCN Fact Sheet citation
Please cite as: de Lange, P.J. (Year at time of access): Abrodictyum caudatum Fact Sheet (content continuously updated). New Zealand Plant Conservation Network. https://www.nzpcn.org.nz/flora/species/abrodictyum-caudatum/ (Date website was queried)