Alternation of generations is the type of life cycle that occurs in those plants and algae in the Archaeplastida and the Heterokontophyta that have distinct haploid sexual and diploid asexual stages. In these groups, a multicellular haploid gametophyte with n chromosomes alternates with a multicellular diploid sporophyte with 2n chromosomes, made up of n pairs. A mature sporophyte produces haploid spores by meiosis, a process which reduces the number of chromosomes to half, from 2n to n.
Mosses, the taxonomic division Bryophyta or the bryophytes, are small, non-vascular flowerless plants that typically form dense green clumps or mats, often in damp or shady locations. The individual plants are usually composed of simple leaves that are generally only one cell thick, attached to a stem that may be branched or unbranched and has only a limited role in conducting water and nutrients. Although some species have conducting tissues, these are generally poorly developed and structurally different from similar tissue found in vascular plants. Mosses do not have seeds and after fertilisation develop sporophytes with unbranched stalks topped with single capsules containing spores. They are typically 0.2–10 cm (0.1–3.9 in) tall, though some species are much larger. Dawsonia, the tallest moss in the world, can grow to 50 cm (20 in) in height.
Bryophytes are an informal group consisting of three divisions of non-vascular land plants (embryophytes): the liverworts, hornworts and mosses. They are characteristically limited in size and prefer moist habitats although they can survive in drier environments. The bryophytes consist of about 20,000 plant species. Bryophytes produce enclosed reproductive structures, but they do not produce flowers or seeds. They reproduce via spores. Bryophytes are usually considered to be a paraphyletic group and not a monophyletic group, although some studies have produced contrary results. Regardless of their status, the name is convenient and remains in use as an informal collective term. The term "bryophyte" comes from Greek βρύον, bryon "tree-moss, oyster-green" and φυτόν, phyton "plant".
The Marchantiophyta are a division of non-vascular land plants commonly referred to as hepatics or liverworts. Like mosses and hornworts, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information.
A sporophyte is the diploid multicellular stage in the life cycle of a plant or alga. It develops from the zygote produced when a haploid egg cell is fertilized by a haploid sperm and each sporophyte cell therefore has a double set of chromosomes, one set from each parent. All land plants, and most multicellular algae, have life cycles in which a multicellular diploid sporophyte phase alternates with a multicellular haploid gametophyte phase. In the seed plants, the largest groups of which are the gymnosperms and flowering plants (angiosperms), the sporophyte phase is more prominent than the gametophyte, and is the familiar green plant with its roots, stem, leaves and cones or flowers. In flowering plants the gametophytes are very reduced in size, and are represented by the germinated pollen and the embryo sac.
Sphagnum is a genus of approximately 380 accepted species of mosses, commonly known as "peat moss", though they are different as peat moss has a more acidic pH level. Accumulations of Sphagnum can store water, since both living and dead plants can hold large quantities of water inside their cells; plants may hold 16 to 26 times as much water as their dry weight, depending on the species. The empty cells help retain water in drier conditions.
Monoicous plants are those species that bear both sperm and eggs on the same gametophyte. Dioicous plants are those that have gametophytes that produce only sperm or eggs but never both. The terms are used largely but not exclusively in the context of bryophytes. Both monoicous and dioicous gametophytes produce gametes in gametangia by mitosis rather than meiosis, so that sperm and eggs are genetically identical with their parent gametophyte. The states of being monoicous or dioicous are called monoicy and dioicy respectively.
Polytrichum commune is a species of moss found in many regions with high humidity and rainfall. The species can be exceptionally tall for a moss with stems often exceeding 30 cm (12 in) though rarely reaching 70 cm (27.5 in), but it is most commonly found at shorter lengths of 5 to 10 cm. It is widely distributed throughout temperate and boreal latitudes in the Northern Hemisphere and also found in Mexico, several Pacific Islands including New Zealand, and also in Australia. It typically grows in bogs, wet heathland and along forest streams.
Polytrichum is a genus of mosses — commonly called haircap moss or hair moss — which contains approximately 70 species that cover a cosmopolitan distribution.
Aulacomnium palustre, the bog groove-moss or ribbed bog moss, is a moss that is nearly cosmopolitan in distribution. It occurs in North America, Hispaniola, Venezuela, Eurasia, and New Zealand. In North America, it occurs across southern arctic, subboreal, and boreal regions from Alaska and British Columbia to Greenland and Quebec. Documentation of ribbed bog moss's distribution in the contiguous United States is probably incomplete. It is reported sporadically south to Washington, Wyoming, Georgia, and Virginia.
Polytrichum juniperinum, commonly known as juniper haircap or juniper polytrichum moss, is an evergreen and perennial species of moss that is widely distributed, growing on every continent including Antarctica.
Itatiella ulei is a species of moss in the family Polytrichaceae. It is the only species in the genus Itatiella. The Polytrichaceae is a common family of mosses that does not have close living relatives. Its small size and the inflexed leaf apex characterize Itatiella ulei. When this species grows directly exposed to sun at high elevations, it presents a similar aspect but can be distinguished based on the distal lamella cells which are single and rhombic.
Hypnodendron comosum, commonly known as palm moss or palm tree moss, is a ground moss which can be divided into two varieties: Hypnodendron comosum var. comosum and Hypnodendron comosum var. sieberi. Both Hypnodendron varieties most commonly grow in damp locations in the temperate and tropical rainforests of New South Wales, Victoria, and Tasmania in southern Australia and in New Zealand.
Splachnaceae is a family of mosses, containing around 70 species in 6 genera. Around half of those species are entomophilous, using insects to disperse their spores, a characteristic found in no other seedless land plants. Many species in this family are coprophilous, growing exclusively on animal faeces or carrion. For this reason, certain genera such as Splachnum Hedw. are often referred to as "dung mosses."
Pogonatum urnigerum is a species of moss in the family Polytrichaceae, commonly called urn haircap. The name comes from "urna" meaning "urn" and "gerere" meaning "to bear" which is believed to be a reference made towards the plant's wide-mouthed capsule. It can be found on gravelly banks or similar habitats and can be identified by the blue tinge to the overall green colour. The stem of this moss is wine red and it has rhizoids that keep the moss anchored to substrates. It is an acrocarpous moss that grows vertically with an archegonium borne at the top of each fertilized female gametophyte shoot which develops an erect sporophyte.
Climacium dendroides, also known as tree climacium moss, belongs in the order Hypnales and family Climaciaceae, in class Bryopsida and subclass Bryidae. It is identified as a "tree moss" due to its distinctive morphological features, and has four species identified across the Northern Hemisphere. The species name "dendroides" describes the tree-like morphology of the plant, and its genus name came from the structure of the perforations of peristome teeth. This plant was identified by Weber and Mohr in 1804. They often have stems that are around 2-10 cm tall and growing in the form of patches, looking like small palm-trees. They have yellow-green branches at the tip of stems. The leaves are around 2.5-3 mm long, with rounder stem leaves and pointier branch leaves. Their sporophytes are only abundant in late winter and early spring, and appears as a red-brown shoot with long stalk and cylindrical capsules.
Sphagnum papillosum, the papillose peatmoss, is a species of peat moss distributed throughout the northern hemisphere. Although sometimes confused with Sphagnum imbricatum and Sphagnum palustre, it is distinguished by its yellow-green to brown short, blunt branches and papillose chlorophyllose cells.
Ulota is a genus of mosses comprising 69 species with a worldwide distribution, though most species are found in the southern hemisphere.
Plagiomnium venustum, also known as magnificent leafy moss, is a species of moss belonging to the family Mniaceae. It is found mainly in western North America along the coastal region. This moss can be identified from other members of the Plagiomnium genus by dark coloured stomata guide cells and the absence of sterile stems. It is most commonly found growing as a mat on a variety of substrate, but mainly on humus and moist soil.
Andreaea rupestris is a species of moss in the class Andreaeopsida, are commonly referred to as the "lantern mosses" due to the appearance of their dehisced sporangia. It is typically found on smooth, acidic, exposed rock in the Northern hemisphere. It exhibits the common features of the genus Andreaea such as being acrocarpous, having dark pigmentation, lacking a seta, and bearing 4 lines of dehiscence in its mature sporangia, but can be further identified upon careful examination of its gametophytic leaves which have an ovate base to a more blunt apex compared to other similar species.
