The genus Plagiochila, with more than 1600 published binomials and
about 400 to 450 species worldwide, belongs to one of the largest
genera of the hepatics. The rather monotonous morphology and high
plasticity especially of leaf cell patterns, leaf dentation, leaf
position, and leaf shape causes great problems in identifying the
species, and several attempts have been done, to subclassify the
genus. Even the most comprehensive classification by Carl (1931)
remains provisional, causing great confusion. A world-wide approach
therefore is urgently required for understanding this large and
difficult genus and its allies.
Jochen Heinrichs from Göttingen started with this huge and nearly
insoluble task, revising as a first step the neotropical Plagiochila
species. Nearly 850 taxa are described from tropical America, that in
his opinion may belong to 100-120 species. In the present work, a
taxonomic revision of Plagiochila sect. Hylacoetes, sect. Adian-
thoideae and sect. Fuscoluteae is presented, including a new
classification of the group into nine monophyletic lineages. The study
is based on molecular data (nrITS region), new morphological
characters (e.g., capsul wall epidermis, oil bodies, surface waxes)
and chemical investigations.
After an introduction and historical part, material & methods
(phytochemistry, DNA extraction, PCR amplification, sequencing,
selection of characters), the morphology and anatomy (stem structure
and branching, leaves, underleaves, oil bodies, asexual reproduction,
androecia, gynoecia, sporophyte, spores and elaters) are described.
All taxonomic characters employed are treated in detail. Following is
the phylogeny and sectional classification in nine lineages based on
nrITS sequences of 38 species. These nine lineages are supported by
high bootstrap percentage values, often assignable to morphological
and phytochemical defined sections. Also problems were not ignored:
e.g., the problems of intra-individual ITS polymorphism, as
demonstrated for vascular plants, or interspecific hybridization and
reticulate evolutionary phenomens are discussed, that makes a general
applicability of the ITS region for phylogenetic analysis
problematical. The first part of the study is finished by an overview
and description of these nine sections, including the differentiating
characters in tabular form.
The main part of the book is the taxonomic treatment of the three
independant lineages assignable to sect. Hylacoetes,
sect. Adianthoideae, and sect. Fuscoluteae. The main diagnostic
characters of these are:
P. sect. Hylacoetes: characterized by the absence of surface wax, a
capsule wall epidermis without thickenings on the cell walls and
usually fan-shaped terminal androecia with bracts not overlaping
dorsally. This section comprises 18 species, among them the former
monospecific genera Szweykowskia and Steereochila, that clearly nested
in the molecular analysis within the P. sect. Hylacoetes clade.
P. sect. Adianthoideae: characterized by the absence of surface wax, a
capsule wall epidermis with thickenings on the cell walls and simple,
intercalary androecia with bracts overlaping dorsally. Here, four
species are included.
P. sect. Fuscoluteae: characterized by the presence of surface wax, a
capsule wall epidermis with thickenings on the cell walls and simple,
intercalary androecia with bracts not overlaping dorsally. This
section comprises nine species.
Within each section a dichotomous key is given and each species is
fully described. As might be expected, many species have an extensive
synonymy. The detailed specific descriptions of the gametophyte and
sporophyte are accompanyied by line drawings of all, but one species
(P. rudischusteri; 46 plates), citation of representative specimens
examined, distributional and ecological notes. The descriptions and
illustrations are very good and serves its purpose well. Highly
welcome are the remarks on differentiation and variation of the
species. Beside one new species, P. patriciae from Costa Rica, the
study includes three new combinations [comb. & stat. nov.: P.
dimorpha var. ecuadorica (= Steereochila ecuadorica), P. superba
var. macrotricha (= P. macrotricha), and P. heterophylla
var. beauverdii (= P. beauverdii)] and about 77 taxa are brought to
synonymy. 12 plates based on SEM studies of surface wax structures,
spores and elaters add to the excellent overall impression. Up to now,
60 Neotropical Plagiochila species can be differentiated, which
represent about half of the expected number of species. The present
treatment includes 31.
As a further main result of the study, P. sect. Subplanae now is
treated as a synonym of the former palaeotropical section Cucullatae,
due to the similarities in morphology (capsule wall structure) and the
molecular analysis. This leads to a range extension of this section to
the Neotropics. Its single representant in the Neotropics is P.
subplana.
Revising a notoriously difficult genus such as Plagiochila is
certainly no piece of cake. It seems to me, that Heinrich has done a
very good work and progressing well in revising neotropical
Plagiochilas. With this excellent, thoroughness and com- prehensiness
account on the neotropical species, Heinrichs therefore fills a huge
gap. But the work has also shown, that natural groups (monophyletic
lineages) of neotropical Plagiochilas often have no autapomorphisms.
Therefore they can be identified only on the basis of tendencies of
characters. Absolute diagnostic characters are infrequent. The
quality of a revision must be measured by the working ability of the
identification keys. I was not able to test the keys completely, but
I have the feeling, that the identification of neotropical
Plagiochilas will be not easy, also in future. Nevertheless, this
revision is urgently needed and is a must for bryologists, especially
those working in the Neotropics.
HARALD KÜRSCHNER, Berlin
Nova Hedwigia vol. 76, no. 1-, pp. 269-271
