Original paper
On Takakia and the phylogenetic relationships of the Takakiales
Schuster, R.M.
Nova Hedwigia Band 64 Heft 3-4 (1997), p. 281 - 310
66 references
published: Sep 22, 1997
DOI: 10.1127/nova.hedwigia/64/1997/281
ArtNo. ESP050006403000, Price: 29.00 €
Abstract
Takakia Hatt. & Inoue is one of a handful of isolated and unique plants discovered in this century whose discovery initiated a considerable and still controversial literature dealing with the larger problem of bryophyte phylogeny. Initially it was questionable whether it was a green alga (Persson), a bryophyte or whether it represented some wholly isolated division. While only gametophytes were known, it was assumed that perhaps a distinct class of bryophytes was involved (Schuster; Mizutani); it has also been placed as an order of Hepaticae, allied to the Calobryales (Hattori & Mizutani; Schuster; Hattori et al.) or merely as a genus of the Calobryales (Proskauer), or a suborder of Calobryales (Schuster); or even as forming a separate division Takakiophyta by Crandall-Stotler. Mizutani regards it as forming a subclass, Takakiidae, within the class Bryopsida. Discovery of ♂️ plants and sporophytes led to a re-appraisal of the status of the Takakiales; Smith and Davison placed Takakia into the Andreaeopsida and stated there is "compelling evidence that it is a moss... ". Evaluation of these irreconcilable opinions suggests that Takakia exhibits a unique "mix" of features found scattered in unrelated Hepaticae: a longitudinal suture of the capsule, as in Monoclea (Monocleales); a feeble conducting strand of the sporophyte, as in Monoclea; 2-4-lobed leaves, as in many Jungermanniales; absence of rhizoids linked with development of leafless stoloniform axes and geotropic leafless axes, shared with Calobryales; orange antheridia found in axils of all three rows of leaves, as in Calobryales; a histologically rather simple seta, as in many Jungermanniales; a 3-4-5-layered capsule wall with thickened epidermal cells but thin inner cell strata, devoid of stomata and of air spaces, as in Symphyogyna (Metzgeriales); conspicuous slime papillae, secreting massive quantities of mucilaginous matter, as in Calobryales and, i. a. Verdoornia and Treubia (Metzgeriales). Other criteria are clearly as in Musci (a calyptra that ruptures as the distal portions are elevated on the capsule; sporogenesis after seta elongation ceases; a capsule that differentiates after the seta elongates; a persistent seta and durable sporophyte generation; lack of elaters; presence of a feeble columella; a mosslike antheridial ontogeny; axillary hairs not associated with gametangia, and gametangial anatomy). Gametophytic criteria are more suggestive of a hepatic affinity; sporophytic criteria, on balance, are more mosslike. This peculiar "mix" of criteria is regarded as prohibiting placing Takakia into either group. The genus is regarded as forming a wholly isolated class, Takakiopsida, showing remote similarities to Calobryales is regarded as forming a wholly isolated class, Takakiopsida, showing remote similarities to Calobryales (Hepaticae or Hepaticopsida) and Andreaeopsida. Most significantly the convergence of Takakia to both groups clearly supports the acceptance of Bryophyta as a natural phylogenetic unit.
Keywords
bryophyte phylogeny • green alga • gametophytes • moss