Classification
Class
Polypodiopsida
Subclass
Polypodiidae
Order
Polypodiales Link
Family
Blechnaceae Newman
Genus
Blechnum L.
 Nomenclature
Scientific Name:
Blechnum ×aggregatum (Colenso) Tindale, Proc. Linn. Soc. New South Wales 85: 254 (1960)
Synonymy:
  • ≡ Lomaria aggregata Colenso, Trans. & Proc. New Zealand Inst. 20: 223 (1888)
  • ≡ Austroblechnum ×aggregatum (Colenso) Gasper & V.A.O.Dittrich in Gasper et al., Phytotaxa 275: 203 (2016)
Holotype: New Zealand, com. W. Colenso 5/1890, K 001092695!
Etymology:
From the Latin aggregatus (clustered together), a reference to the growth habit of the original collection, with several plants growing together from one root-stock.
 Recognition

Blechnum ×aggregatum is the hybrid between B. chambersii and B. membranaceum, usually arising wherever the two species occur together, and characterised by its intermediate morphology. It is more easily recognised in the field than in the herbarium, possibly because the differences between the hybrid and its two parents are more obvious in live material. The fronds are of intermediate size and outline, but hybrid plants can sometimes be recognised by having relatively narrow, obovate sterile laminae, similar to those of B. membranaceum, but fertile fronds that are equal to or shorter than the sterile ones, like those in B. chambersii. Spores of both species have a very smooth perine (Large & Braggins 1991), and hybrid plants usually have spores of normal appearance. Only very rarely are malformed spores seen (e.g. WELT P001231, Pukeatua).

 Biostatus
Indigenous (Endemic)
 Notes

Blechnum chambersii and B. membranaceum are morphologically and genetically very similar. They differ by only one base pair (Shepherd et al. 2007). It is quite possible that hybrids have some degree of inter-fertility, and that hybrid swarms may include F1 and back-cross hybrids, along with the parent species. This requires further investigation.

 Bibliography
Brownsey, P.J.; Perrie, L.R. 2021: Blechnaceae. In: Breitwieser, I. (ed.) Flora of New Zealand — Ferns and Lycophytes. Fascicle 29. Manaaki Whenua Press, Lincoln.
Colenso, W. 1888: On newly discovered and imperfectly known ferns of New Zealand, with critical observations. Transactions and Proceedings of the New Zealand Institute 20: 212–234.
Gasper, A.L. de; Dittrich, V.A.O.; Smith, A.R.; Salino, A. 2016: A classification for Blechnaceae (Polypodiales: Polypodiopsida): New genera, resurrected names, and combinations. Phytotaxa 275(3): 191–227.
Large, M.F.; Braggins, J.E. 1991: Spore atlas of New Zealand ferns and fern allies. SIR Publishing, Wellington.
Shepherd, L.D.; Perrie, L.R.; Parris, B.S.; Brownsey, P.J. 2007: A molecular phylogeny for the New Zealand Blechnaceae ferns from analyses of chloroplast trnL-trnF DNA sequences. New Zealand Journal of Botany 45: 67–80.
Tindale, M.D. 1960: Contributions to the flora of New South Wales: new species and combinations in Acacia and Blechnum. Proceedings of the Linnean Society of New South Wales 85: 248–255.