Classification of brayophyta

General characters of brayophyta, Classification according to G.M.Smith

1. Bryophyte ( Bryon- moss + phyte -Plant) V.S.Patil Associate Professor, Department of Botany Shri Shivaji College of Arts, Commerce,& Science Akola

2. Hornworts Liverworts Mosses 

3. Bryophyte , traditional name for any nonvascular seedless plant —namely, any of the  mosses (division Bryophyta ), hornworts (division Anthocerotophyta ), and liverworts (division Marchantiophyta ). Most bryophytes lack complex tissue organization, yet they show considerable diversity in form and ecology . The first evidence marking the emergence of bryophytes appears in rocks collected from Argentina that date to the early part of the  Ordovician Period (485.4 million to 443.8 million years ago). Habit- Bryophytes often grow profusely, forming deep, soft carpets on forest floors and over rock surfaces, sheathing trunks and branches of trees and shrubs, and festooning branches. 

4. Habit & Habitat

5. Distribution and abundance Bryophytes are distributed throughout the world , from polar and alpine regions to the tropics. Water must, at some point, be present in the habitat in order for the sperm to swim to the egg. Bryophytes do not live in extremely arid sites or in seawater , although some are found in perennially damp environments within arid regions and a few are found on seashores above the intertidal zone . A few bryophytes are aquatic. Bryophytes are most abundant in climates that are constantly humid and equable . The greatest diversity is at tropical and subtropical latitudes . Bryophytes (especially the moss  Sphagnum ) dominate the vegetation of peatland in extensive areas of the cooler parts of the Northern Hemisphere .

6. General Features- Some liverworts and hornworts have a flattened gametophyte, called a  thallus . The thallus tends to be ribbonlike in form and is often compressed against the substratum to which it is generally attached by threadlike structures called rhizoids. Rhizoids also influence water and mineral uptake. Thallus bryophytes vary in size from a length of 20 cm (8 inches) and a breadth of 5 cm (2 inches; the liverwort  Monoclea ) to less than 1 mm (0.04 inch) in width and less than 1 mm in length (male plants of the liverwort  Sphaerocarpos ). The thallus is sometimes one cell layer thick through most of its width (e.g., the liverwort  Metzgeria ) but may be many cell layers thick and have a complex tissue organization (e.g., the liverwort  Marchantia ). Branching of the thallus may be forked, regularly frondlike , digitate , or completely irregular. The margin of the thallus is often smooth but is sometimes toothed; it may be ruffled, flat, or curved inward or downward .

7. Leafy bryophytes grow up to 65 cm (2 feet) in height (the moss  Dawsonia ) or, if reclining, reach lengths of more than 1 metre (3.3 feet; the moss  Fontinalis ). They are generally less than 3 to 6 cm (1.2 to 2.4 inches) tall, and reclining forms are usually less than 2 cm (0.8 inch) long. Some, however, are less than 1 mm in size (the moss  Ephemerum ). Leaf like structures, known as  phyllids , are arranged in rows of two or three or more around a shoot or may be irregularly arranged (e.g., the liverwort  Takakia ). The shoot may or may not appear flattened. The phyllids are usually attached by an expanded base and are mainly one cell thick. Many mosses, however, possess one or more midribs several cells in thickness. The phyllids of bryophytes generally lack vascular tissue and are thus not analogous to the true leaves of vascular plants.

8. Most gametophytes are green, and all except the gametophyte of the liverwort  Cryptothallus  have  chlorophyll. Many have other pigments, especially in the cellulosic cell walls but sometimes within the cytoplasm of the cells. Bryophytes form flattened mats, spongy carpets, turfs, or festooning pendants . These growth forms are usually correlated with the humidity and sunlight available in the habitat . The  thalli  of most liverworts and hornworts consist of relatively undifferentiated layers of cells. Those cells on the dorsal surface are rich in chlorophyll , while those situated deeper within the thallus lack chlorophyll but have storage products of photosynthesis, especially  starch.

9. Reproduction and life cycle The life cycle of bryophytes consists of an alternation of two stages, or generations , called the   sporophyte  and the  gametophyte . Each generation has a different physical form. When a spore germinates, it usually produces the protonema , which precedes the appearance of the more elaborately organized gametophytic  plant, the gametophyte, which produces the sex organs . The  protonema  is usually threadlike and is highly branched in the mosses but is reduced to only a few cells in most liverworts and hornworts. The protonema stage in liverworts is usually called a sporeling in other bryophytes.

10. Vegetative Reproduction- The gametophyte of some bryophyte species reproduces asexually, or vegetatively , by specialized masses of cells ( gemmae ) that are usually budded off and ultimately give rise to gametophytes. Fragmentation of the gametophyte also results in vegetative reproduction: each living fragment has the potential to grow into a complete gametophyte. Fragmentation Gemmae

11. Asexual reproduction - Sporophytes of mosses usually consist of the foot, which penetrates the gametophore , the  seta , with an internal conducting system, and a terminal sporangium. The seta contains chlorophyll when immature and cannot absorb moisture from the environment because its surface is covered by a water-impermeable layer, the cuticle. The  sporophyte  is photosynthetic when immature, but its restricted amount of chlorophyll-containing tissue rarely produces enough carbohydrates to nourish a developing sporangium. All water and much of the needed nutrients are absorbed from the gametophore and are conducted through the transfer tissue of the foot up the conducting strand that leads to the apex of the sporophyte . The seta is made rigid by thick-walled cells external to the conducting strand. The sporangium differentiates after the seta elongates and is protected from injury and drying by the calyptra .

12. The moss sporangium usually opens by way of an apical lid ( the operculum ). When the operculum falls, there is exposed a ring of teeth that controls the release of the spores over an extended period of time. These teeth usually respond to slight moisture changes and pulsate inward and outward, carrying spores out of the sporangium on their jagged inner surfaces . The sporangium usually contains within it elongate cells (elaters) with coiled thickenings that are scattered among the spores. 

13. Sexual Reproduction- The gametophyte—the thallus or leafy stage—is generally perennial and produces the male or female sex organs or both. The female sex organ is usually a flask-shaped structure called the  archegonium . The archegonium contains a single egg enclosed in a swollen lower portion that is more than one cell thick. The neck of the archegonium is a single cell layer thick and sheathes a single thread of cells that forms the neck canal . When mature and completely moist, the neck canal cells of the archegonium disintegrate, releasing a column of fluid to the neck canal and the surrounding water. The egg remains in the base of the archegonium , ready for fertilization . The male sex organ, the  antheridium , is a saclike structure made up of a jacket of sterile cells one cell thick; it encloses many cells, each of which, when mature, produces one sperm .

14. The antheridium is usually attached to the gametophyte by a slender stalk. When wet, the jacket of the mature antheridium ruptures to release the sperm into the water. Each sperm has two flagella and swims in a corkscrew pattern. When a sperm enters the field of the fluid diffused from the neck canal, it swims toward the site of greatest concentration of this fluid, therefore down the neck canal to the egg. Upon reaching the egg, the sperm burrows into its wall, and the egg nucleus unites with the sperm nucleus to produce the diploid  zygote. The zygote remains in the archegonium and undergoes many  mitotic cell divisions  to produce an embryonic sporophyte . The lower cells of the archegonium also divide and produce a protective structure, called the  calyptra , that sheathes the growing embryo.

15. As the sporophyte enlarges, it is dependent on the gametophore for water and minerals and, to a large degree, for nutrients manufactured by the gametophyte. The water and nutrients enter the developing sporophyte through the tissue at its base, or foot, which remains embedded in the gametophyte. Mature bryophytes have a single  sporangium  (spore-producing structure) on each sporophyte . The sporangium generally terminates an elongate stalk, or seta, when the sporangium is ready to shed its spores. The sporangium rupture usually involves specialized structures that enhance expulsion of the spores away from the parent gametophyte.

16. Alternation of generations- The bryophytes show an alternation of generations between the independent  gametophyte generation, which produces the sex organs and sperm and eggs , and the dependent  sporophyte  generation, which produces the spores . (produces only one spore-containing organ , sporangium ).   In bryophytes the long-lived and conspicuous generation is the gametophyte. Structures resembling stems, roots, and leaves are found on the gametophore of bryophytes. The sporophyte releases spores, from which the gametophytes ultimately develop.    

17. Economic importance- 1.The   peat moss  genus  Sphagnum used in horticulture, as an energy source (fuel), and, to a limited extent, in the extraction of organic products, in whiskey production, and as insulation . 2. Bryophytes are very important in initiating soil formation on barren terrain, in maintaining soil moisture, and in recycling nutrients in forest vegetation . 3. In research- in areas of genetics and cytology .

18. Classification of Bryophyte By G.M.Smith

19. Division Bryophyta Class 3.   Musci  (mosses)/ Brayopsida Subclass1. Sphagnidae Order1- Sphagnales Subclass2. Andreaeidae Order 1- Andreaeales Subclass 3. Bryidae Order1- Polytrichales Order2- Funariales Class2.  Anthocerotae  (hornworts)/ Anthoceropsida Class 1.  Hepaticae  (liverworts)/ Hepaticopsida Order 1.  Sphaerocarpales Family 1.  Sphaerocarpaceae Family 2.  Riellaceae Order 2.  Marchantiales Family 1.  Ricciaceae Family 2.  Corsiniaceae Family 3.  Targioniaceae Family 4.  Monocleaceae Family 5.  Marchantiaceae Order 3.  Jungermanniales Suborder 1.  Metzgerineae Suborder 2.  Jungermanninea e Order 4.  Calobryales Order 1-Anthocerotales

20. Hepaticae :  A class of Bryophyta comprising the liverworts and being distinguished from Musci by the presence of a usually thalloid gametophyte  that is not produced from a protonema , unicellular rhizoids and elaters and antheridia and archegonia  that are borne on the thallus and produce a short-lived and simple sporophyte . Anthocerotae :   The Anthocerotae (hornworts) is one class of the Division Bryophyta (bryophytes) and consists of a single order,  Anthocerotales , and a single family, Anthocerotaceae .  The better known classes of the Bryophyta are the Musci (mosses) and Hepaticae (liverworts). Musci :  A class of Bryophyta comprising the mosses and being characterized by a well-developed leafy gametophyte that arises by budding from a protonema and bears sex organs among the leaves at its tip and by a  sporophyte that develops from the fertilized egg,  remains attached to the tip of the gametophyte, and is a naked usually stalked and operculate capsule in which asexual spores are borne.

21. Class I- Hepaticae / Hepaticopsida (Liverworts) (4 orders, 9 families, 225 genera and 8,500+- species) The gametophytes are dorosiventrally differentiated. They may be thalloid ( thallose ) or differentiated into leaves and stem (foliose). Leaves, if present, are without mid-rib and are arranged into two or tghree rows on the axis. The dehiscent mechanism of capsules is indefinite and irregular. The sporophyte may be simple, or differentiated into foot and capsule, or into a foot seta and capsule, The sporogenous cells develop from the endothecium of sporogonium . The sporophyte is completely dependent on gametophytes for its nutritive supply. The wall of sporogonium is one to several layered thick. The stomata are not present on the wall of sporogonium . Order - Sphaerocarpales (3 genera and 2 families) Order – Marchantiales (32 genera and 400 species) Order – Jungermanniales (220 genera and 8,500 species) Order – Calobryales (2 genera and 9 species)

22. Class II- Anthocerotae / Anthocerotopsida (Hornworts): (1 orders, 2 families, 6 genera and 301+- species) The gametophyte is thalloid and dorsiventral , bearing simple and smooth-walled rhizoides ; tuberculate rhizoids and ventral scales are altogether absent. Thallus is homogenous internally. Each cell of the thallus is provuded with a hloroplast , a nucleus and a pyrenoid body. Pyrenoid body includes several granules. The wall of capsule is 4-6 layers of cells thick, and is provided with stomata. The basal portion of capsule is meristematic . It divides continuously to add to the upper portion.

23. The sex organs are found to be embedded in the gametophytic tissue. Sporogenous mass evolve form amphithecium and arches over the columella . The antheridia arise from the hypodermal cell of the thallus on the dorsal side of it; they develop within the antheridial chambers. The archegonia are found in sunken conditions on the dorsal side of the thallus , they develop from superficial cells. Family – Anthocerotaceae (4/5 genera) Family – Notothylaceae (Single genus – Notothylas )

24. Class III – Musci / Bryopsida (Mosses): (3 orders, 28 families, 660 genera and 14504+- species) The plants have well differentiated structures including axis, leaves and multicellular rhizoids. The leaves are arranged in 3-8 rows on the axis. Each leaf has a mid-rib. The wall of the capsule consists of many layers of chlorophyllous cells and stomata. sex organs develop on apical portion of stem. The sporophyte is differentiated into foot, seta and capsule. The sporogenous mass or archesporium develops from the outer layer of endothecium . Endothecium also forms columella . The eleters are not present in the sporogonium

25. Sub-class I – Sphagnidae / Spagnobrya (1 order, 1 family, 1 genus Sphagnum, 326 species) Order1- Sphagnales Sub-class II – Andreaeidae / Andreaeobrya (1 order, 1 family) Order 1- Andreaeales Sub-class III – Bryidae / Eubrya (650 genera, 14,000 species) Order I – Polytrichales (1 family, important genera – Polytrichum & Pogonatum ) Order II – Funariales (26 genera and 356 species)