In this article we will discuss about the classification of bryopsida.
In such a vast group, naturally, there are many variations so that classification is difficult. Structures of both gametophytes and sporophytes have to be considered and in mosses these two phases have attained specialisation in different degrees in the different species.
Thus, it is not possible to arrive at a phylogenetic system based on a strict parallel evolution of both gametop hyte and sporophyte. But, just as in the Angiosperms the flower characters are considered more reliable in classification, in Bryidae the sex organs and the sporophyte are considered more important in any general classification.
On the other hand, a system based only on sporophytes ignoring the gametophytes altogether also becomes artificial and not properly phylogenetic in understanding the modern trend of moss taxonomy.
The following systems of classification may be considered as important in understanding the modern trend of moss taxonomy:
(i) Hedwig’s System (1801):
The really first attempt at a natural system of classification of mosses was by J. Hedwig in his Species Muscorum (1801). He arranged the genera (only 35 were known at that time) mainly on the peristome and a few other sporophytic characters. The system is no longer followed as it is clumsy and has also become artificial as the gametophytic characters have been ignored altogether.
Thus, such widely differing genera as Funaria and Hypnum have been placed close together. Yet, his genera are so well defined that most of them stand even today. His work is, therefore, considered as the starting point of modern Musicology.
According to International Rules, the nomenclature of mosses (with the exception of Sphagnum which alone starts with Linnaeus) starts with Hedwig’s Species Muscorum. All previous names are to be considered invalid.
(ii) Bridel (1826) and Bryologia Europaea (1836—1855):
S. E. Bridel (1826) suggested division of the Bryidae into Acrocarpi (erect plants with apical sporophytes) and Pleurocarpi (prostrate, branching plants with numerous sporophytes on short lateral branch tips). P. Bruch, W. P. Schimper and T. Guembal-adopted this division in their Bryologia Europaea (1836-1855) and elaborated the system of classification rendering it more natural than in Hedwig.
(iii) Mueller (1849):
C. Mueller, in his Synopsis Muscorum Frondosorum (1849), divided the true mosses into Gleistocarpi (no organised annulus, peristome or operculum; dehiscence of capsules by rupture or decay of jacket) and Stegocarpi (regular annulus and operculum, spore dispersal usually by peristome).
(iv) Mitten (1859):
W. Mitten, who wrote the only Bryological Flora of India, divided the Bryidae into the Arthrodonti (articulate thin peristome teeth) and the Nematodonti (wormlike solid peristoma teeth) in his Musci indiae orientaiis (1859). The spellings got changed later on. This was the first real attempt to classify mosses according to the nature of the peristomes.
(v) Lindberg (1879):
Classification of the common mosses into the Cleistocarpi and the Stegocarpi was soon found, to be artificial. Excepting in Archidium, all cleistocarpic genera were found to be connected to some stegocarpic genera by their manner of development. S. O. Lindberg distributed these cleistocarpic genera among the various stegocarpic families in his Musci scandinavici (1879).
(vi) Philibert (1884-1902):
Although the importance of the peristomes in the classification of the common mosses was recognised by Mitten, it was the detailed study of the peristomes published in a series of articles by H. Philibert in the Revue bryologique during 1884 to 1902, which clearly showed that these mosses could be fully classified better by laying a greater stress on the peristome structure.
He further classified the Arthrodonteae into (1) Haplolepideae and (2) Diplolepideae. He also considered the distinctiveness of Encalyptaceae which contains the characters of the Haplolepideae and the Diplolepideae and even some characters of the Nematodonteae. He, therefore, suggested that the Encalyptaceae may be the starting point of the Haplolepideae and the Diplolepideae.
(vii) Fleischer (1906—1908):
The first really phylogenetic classification of mosses laying importance on sporophytic characters but not ignoring the gametophytic characters was adapted by M. Fleischer in the Musci der Flora von Buitenzorg Vol. II (1906—1908). This is the system which was later adapted by V. F. Brotherus in Engler’s Pflanzenfamilien (described below).
(viii) Cavers (1910—1911):
Cavers directly divided the Bryophytes into ten groups or ‘orders’ –“The Interrelationships of the Bryophyta” published in New Phytologist, 1910—1911) the last four of which (Tetraphidales, Polytriechales, Buxbaumiales and Eubryales) comprise the Bryidae as we understand it today.
Accepting the findings of Philibert, Cavers classified them as follows:
A. Nematodonteae
I. Tetraphidales
II. Polytrichales
III. Buxbaumiales
B. Arthrodonteae
IV. Eubryales:
Series 1. Haplolepideae (Peristome teeth in a single ring. The teeth are formed by membranes belonging to two concentric cell layers. Each tooth formed by a single row of external plates and two rows of internal plates, lepos = scale).
Cohort i. Archidioideae (Cleistocarpic) —Archidiaceae.
Cohort ii. Dlcranoidea; (Teeth cleft into two or three) —Dicranaceae, Fusidentaceae, Leucobryaceae.
Cohort iii. Monocranoideae (Teeth undivided) — Leucophanaceae, Syrrhopodontaceae, Calymperaceae.
Cohort iv. Ditrichocranoideae (Teeth deeply divided into two, three or more filaments) —Trematodontaceae, Angstroemiaceae, Ditrichaceae, Trichosto- maceae.
Cohort v. Platycranoideae (Teeth broad and usually undivided, may be perforated by slits, rarely split into two or three) —Seligeriaceae, Grimmiaceae.
Series 2. Heterolepideae (Peristome teeth variable, haplolepideous or diplolepideous) —Encalyptaceae.
Series 3. Diplolepideae (Peristome teeth normally in two rings. Outer ring (exostome) teeth with two rows of external plates. Inner ring (endostome) teeth formed of thin plates, their outer layer corresponding to the inner layer of the exostome).
Subseries i. Epicranoideae (Exostome teeth superposed on endostome processes)
—Funarineae, Splachnineae.
Subseries ii. Metacranoideae (Exostome teeth alternating with endostome processes)
—Bryinae, Isobryinae, Hookerinae, Hypnobryinae.
This system was followed by Campbell and forms the basis of the classification proposed by Dixon. It is certainly a high scientific system and has been adapted in this book after some modifications to bring it into line with the families as they are known today. Figure 462 shows the peristome structures of the main groups of Bryidae.
(9) Fleischer’s system as adapted by V. F. Brotherus in Engler’s Pflanzenfamilien (2nd Edn., 1924).
Subclass Bryales (=Bryidae)
Reihengruppe (Cohort) I. Eubryinales (=Eubryiidae)
Reihe (Orders): 1. Fissidentales, 2. Dicranales, 3. Pottiales, 4. Grimmiales, 5. Funariales, 6. Schistostegales, 7. Tetraphidales, 8. Eubryales, 9. Isobryales, 10. Hookeriales, 11. Hypnobryales.
Reihengruppe (Cohort) II. Buxbaumiinales (—Buxbaumiidae)
Reihe (Order) 12. Buxbaumiales. Reihengruppe
(Cohort) III. Polylrichinales (=Polytrichiidae) Reihe
(Orders): 13. Polytrichales, 14. Dawsoniales.
The names in brackets are modifications according to the International Code of Nomenclature.
(ix) Dixon’s (1932) System:
Although following Fleischer’s System for the orders, Dixon laid greater stress on the structure of the peristome in the broader groupings following the system developed by Mitten, Philibert and Cavers. He also supported Cavers by bringing the Nematodonteae to the first position instead of the last. This classification, is, no doubt very natural although his use of the term ‘clan’ is not happy.
The general classification is as follows:
Subclass BRYALES:
Clan. I. Nematodonteae (Peristome teeth solid, formed of longitudinal fibres derived from concentric layers of cells of the capsule).
Orders: 1. Tetraphidales, 2. Calomniales, 3. Schistostegales, 4. Buxbaumiales, 5. Polytrichales.
Clan II. Arthrodonteae (Peristome teeth thin, membranous, articulated).
Subclan i. Haplolepideae
Orders: 6. Fissidentales, 7. Grimmiales, 8. Dicranales., 9. Syrrhopodontales, 10. Pottiales.
Subclan ii. Heterolepideae
Order: 11. Encalyptales
Subclan iii. Diplolepideae
Orders: 12. Orthotrichales, 13. Funariales, 14. Eubryales, 15. Isobryales, 16. Hookeriales, 17. Hypnobryales.
While the orders up to Heterolepideae are acrocarpous, the Diplolepideae begins in acrocarpous and ends in pleurocarpous forms. The acrocarpous teeth show vertical striations while the pleurocarpous striation is horizontal.
(x) Reimer’s (1954) System in Engler’s Syllabus der Pƒlanzenfamilien (12th Edition):
Reimers has suggested that the three Cohorts in Brotherus’ System should be raised to subclasses parallel with Sphagnidae and the Andreaeideae. He names these subclasses (1) Bryidae (= Eubryinales), (2) Buxbaumiidae (= Buxbaumiinales) and (3) Poly- trichidae (—Polytrichinales). He also increases the number of Orders to 15 by raising the family Archidiaceae to the first order Archidiales in conformity with Cavers.
(12) Cronquist, Takhtajan and Zimmermann (1966) divided the Plant Kingdom into the Subkingdoms Thallobionta and Embryobionta. Within the Embryobionta are the Divisions Bryophyta (without tracheaea) and the Trachaeophytic Divisions. The Division Bryophyta is divided into Subdivisions of which Muscophytina (=Bryo- psida) is one.
This Subdivision is divided into four classes (1-) Sphagnopsida (—Sphagnidae), (2) -Andreaeopsida ( —Andreaeidae), (3) Archidiopsida ( =Archidiales here) and (4) Peri- stomiopsida (Bryidae without Archidiales).
In the following account of the Indian mosses (arranged according to a new modification of Cavers, Brotherus, Dixon and Reimers systems) the number of species occurring in the Indian subcontinent, Burma and Ceylon is given within brackets after the name of each genus. Families and genera not represented in this area have been omitted.