Conceptacle
Encyclopedia
Conceptacles are specialised cavities of marine and freshwater algae
that contain the reproductive organs. They are situated in the receptacle and open by a small ostiole
. Conceptacles are present in Corallinaceae
, and Hildenbrandiales
, as well as the brown Fucales
. In the Fucales there is no haploid phase in the reproductive cycle and therefore no alternation of generations
. The thallus
is a sporophyte
. The diploid plants produce male (antheridia) and female (oogonia) gametangia by meiosis
. The gamete
s are released into the sea
, after fusion the zygote
settles and begins growth.
Two taxa, the corallines and Hildenbrandiaceae, bear conceptacles, although the striking difference between their formation indicates that the conceptacles are not homologous.
Similar structures also exist: cryptostomata are similar to conceptacles but differ having only hairs and are sterile. Caecostomata, are found only in Fucus distichus, in these the ostiole becomes blocked during development.
This is a central pillar constituting central calcified cells covered by cellular debris. These sterile cells rise up from the conceptacle floor to form a peak.
Some conceptacles form by the centripetal expansion of a hole near the thallus surface; in such cases, a roof forms by nearby filaments arching over and establishing themselves as short (often 1–9 cells long) filaments that cover the chamber, leaving a central pore through which the spores can escape. If these filaments are vicarious they may produce a beak-like opening.
In asexual conceptacles, the spores tend to be large, and so are squeezed in, filling the conceptacle chamber "like orange segments".
These develop where weakly calcified cells break down to produce a cavity. In L. incrustans, Their columella is central and obvious (see above); it is accentuated by the spores (which may be bispores, tetraspores, etc.), which squeeze against the columella and conceptacle walls. Asexual conceptacles may be uniporate or multiporate.
These lack a columella. L. incrustans has distinct male and female plants; the two conceptacle types never co-occur on the same thallus. Male conceptacles tend not to sit as deep within the thallus as female conceptacles; their size is similar although their shape tends to differ. Cells within circular regions within the perithallus lengthen to form sexual conceptacles, leaving long, wefty cells around the walls of the conceptacle. In the male conceptacles of Austrolithon, marginal filaments grow more quickly, bending in over the top of the conceptacle cavity and eventually setting up as distinct filaments that form the conceptacle roof.
These are not associated with tissue demineralization; rather, they start to form at the centre (as a female conceptacle) and develop radially. Being mature female conceptacles, these too lack a columella.
Four different modes of asexual conceptacle formation exist. In Corallina and Bossiella, []
In the coralline Bossiella
, the conceptacle instead forms in the outer layer
. A thickening forms, which separates the outer epithallium
from the underlying cortex; this thickening and the overlying epithallium will end up being the cap of the conceptacle, and the underlying cells will develop to become reproductive initials
. Once the cap is formed, the filamentous cells underneath begin to degrade. The tissue around the edge of the cap grows more quickly. This combination produces a chamber beneath the cap.
, which would imply that this giant land organism was not a simple fungus
(as most paleontologists assume today) but a lichen
.
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
that contain the reproductive organs. They are situated in the receptacle and open by a small ostiole
Ostiole
An ostiole is a small hole or opening through which algae or ascomycetal fungi release their mature spores. The term is also used in higher plants, for example to denote the opening of the involuted fig inflorescence through which fig wasps enter to pollinate and breed....
. Conceptacles are present in Corallinaceae
Coralline algae
Coralline algae are red algae in the order Corallinales. They are characterized by a thallus that is hard because of calcareous deposits contained within the cell walls...
, and Hildenbrandiales
Hildenbrandiales
Hildenbrandiales is an order of crustose forms red alga which bear conceptacles and produce secondary pit-connections. They reproduce by vegetative gemmae as well as tetrasporangia, which are produced inside the conceptacles...
, as well as the brown Fucales
Fucales
Fucales is an order in the brown algae . Members of this order are fucoids. The list of families in Fucales, as well as additional taxonomic information on algae, is publicly accessible at Algaebase....
. In the Fucales there is no haploid phase in the reproductive cycle and therefore no alternation of generations
Alternation of generations
Alternation of generations is a term primarily used in describing the life cycle of plants . A multicellular sporophyte, which is diploid with 2N paired chromosomes , alternates with a multicellular gametophyte, which is haploid with N unpaired chromosomes...
. The thallus
Thallus (tissue)
Thallus, from Latinized Greek θαλλός , meaning a green shoot or twig, is the undifferentiated vegetative tissue of some organisms in diverse groups such as algae, fungus, some liverworts, lichens, and the Myxogastria. Many of these organisms were previously known as the thallophytes, a polyphyletic...
is a sporophyte
Sporophyte
All land plants, and some algae, have life cycles in which a haploid gametophyte generation alternates with a diploid sporophyte, the generation of a plant or algae that has a double set of chromosomes. A multicellular sporophyte generation or phase is present in the life cycle of all land plants...
. The diploid plants produce male (antheridia) and female (oogonia) gametangia by meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
. The gamete
Gamete
A gamete is a cell that fuses with another cell during fertilization in organisms that reproduce sexually...
s are released into the sea
Sea
A sea generally refers to a large body of salt water, but the term is used in other contexts as well. Most commonly, it means a large expanse of saline water connected with an ocean, and is commonly used as a synonym for ocean...
, after fusion the zygote
Zygote
A zygote , or zygocyte, is the initial cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo...
settles and begins growth.
Two taxa, the corallines and Hildenbrandiaceae, bear conceptacles, although the striking difference between their formation indicates that the conceptacles are not homologous.
Similar structures also exist: cryptostomata are similar to conceptacles but differ having only hairs and are sterile. Caecostomata, are found only in Fucus distichus, in these the ostiole becomes blocked during development.
Morphology
Conceptacles can measure from 40–150 μm in diameter in some Hildenbrandiales. Some conceptacles are pits within the thallus, whereas others form raised domes protruding above it. Conceptacles open to the environment via one or many pores, depending on the species and the type of conceptacle.Components
- Columella.
This is a central pillar constituting central calcified cells covered by cellular debris. These sterile cells rise up from the conceptacle floor to form a peak.
- Roof filaments.
Some conceptacles form by the centripetal expansion of a hole near the thallus surface; in such cases, a roof forms by nearby filaments arching over and establishing themselves as short (often 1–9 cells long) filaments that cover the chamber, leaving a central pore through which the spores can escape. If these filaments are vicarious they may produce a beak-like opening.
- Spores.
In asexual conceptacles, the spores tend to be large, and so are squeezed in, filling the conceptacle chamber "like orange segments".
Types of conceptacle
There are a range of different conceptacles, classified according to the nature of the spores that they contain; some species may possess as many as four distinct types. For example, Lithophyllum incrustans bears asexual, male, female and cystocarpic (strictly, a type of female) conceptacles, discussed below.- Asexual conceptacles.
These develop where weakly calcified cells break down to produce a cavity. In L. incrustans, Their columella is central and obvious (see above); it is accentuated by the spores (which may be bispores, tetraspores, etc.), which squeeze against the columella and conceptacle walls. Asexual conceptacles may be uniporate or multiporate.
- Sexual (male / female) conceptacles.
These lack a columella. L. incrustans has distinct male and female plants; the two conceptacle types never co-occur on the same thallus. Male conceptacles tend not to sit as deep within the thallus as female conceptacles; their size is similar although their shape tends to differ. Cells within circular regions within the perithallus lengthen to form sexual conceptacles, leaving long, wefty cells around the walls of the conceptacle. In the male conceptacles of Austrolithon, marginal filaments grow more quickly, bending in over the top of the conceptacle cavity and eventually setting up as distinct filaments that form the conceptacle roof.
- Cystocarpic conceptacles.
These are not associated with tissue demineralization; rather, they start to form at the centre (as a female conceptacle) and develop radially. Being mature female conceptacles, these too lack a columella.
Development
In most coralline algae, a cluster of reproductive cells forms in the middle layer of the alga, and is engulfed by the surrounding tissue, which grows up and over the reproductive cells to form a roof and a uniporate conceptacle. Caps may subsequently develop to protect the opening. However the conceptacle may originate at any depth within the thallus, at the surface layer or at the basal perithallus.Four different modes of asexual conceptacle formation exist. In Corallina and Bossiella, []
In the coralline Bossiella
Bossiella
Bossiella is a genus of coralline algae with 5 recognised species. It reproduces via conceptacles; individual thalli only produce conceptacles of a single sex.- Species :The valid species currently considered to belong to this genus are:...
, the conceptacle instead forms in the outer layer
Cortex (botany)
In botany, the cortex is the outer layer of the stem or root of a plant, bounded on the outside by the epidermis and on the inside by the endodermis. It is composed mostly of undifferentiated cells, usually large thin-walled parenchyma cells of the ground tissue system. The outer cortical cells...
. A thickening forms, which separates the outer epithallium
Epithallium
The epithallium is a layer of many algae which bears the majority of photosynthetic apparatus....
from the underlying cortex; this thickening and the overlying epithallium will end up being the cap of the conceptacle, and the underlying cells will develop to become reproductive initials
Reproductive initials
Reproductive initials are filaments below the cuticle surface of algae and fungi which give rise to the bulbs of spore-producing cells ....
. Once the cap is formed, the filamentous cells underneath begin to degrade. The tissue around the edge of the cap grows more quickly. This combination produces a chamber beneath the cap.
Evolutionary history
Conceptacles appear in the fossil record at least as early as the Silurian. Similar structures have been noted in PrototaxitesPrototaxites
The genus Prototaxites describes terrestrial organisms known only from fossils dating from the Silu-Devonian, approximately 420 to 370 million years ago. Prototaxites formed large trunk-like structures up to wide, reaching in height, made up of interwoven tubes just in diameter...
, which would imply that this giant land organism was not a simple fungus
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
(as most paleontologists assume today) but a lichen
Lichen
Lichens are composite organisms consisting of a symbiotic organism composed of a fungus with a photosynthetic partner , usually either a green alga or cyanobacterium...
.