Conceptacles are specialized cavities of marine and freshwater

algae Algae (; singular alga ) is an informal term for a large and diverse group of photosynthetic eukaryotic organisms. It is a polyphyletic grouping that includes species from multiple distinct clades. Included organisms range from unicellular mic ...

that contain the reproductive organs. They are situated in the receptacle and open by a small ostiole.Boney, A.D. (1969). ''A Biology of Marine Algae''. Hutchinson Educational Ltd, London Conceptacles are present in

Corallinaceae The Corallinaceae are one of the two extant Coralline families of red algae; they are differentiated from the morphologically similar Sporolithaceae by their formation of grouped sporangial chambers, clustered into sori. The Corallinoideae i ...

,Irvine, L.M. and Chamberlain, Y.M. (1994). ''Seaweeds of the British Isles''. Volume 1, Part 2B.

Natural History Museum A natural history museum or museum of natural history is a scientific institution with natural history collections that include current and historical records of animals, plants, fungi, ecosystems, geology, paleontology, climatology, and more. ...

, London. and

Hildenbrandiales Hildenbrandiales is an order of crustose forms red alga which bear conceptacles and produce secondary pit-connections. They reproduce by vegetative gemma (botany), gemmae as well as tetrasporangia, which are produced inside the conceptacles. The ...

, as well as the

brown Brown is a color. It can be considered a composite color, but it is mainly a darker shade of orange. In the CMYK color model used in printing or painting, brown is usually made by combining the colors orange and black. In the RGB color model us ...

Fucales The Fucales (fucoids) are an order in the brown algae (class Phaeophyceae). The list of families in the Fucales, as well as additional taxonomic information on algae, is publicly accessible at Algaebaseref name="Guiry and Guiry">Guiry, M.D. and ...

. In the Fucales there is no haploid phase in the reproductive cycle and therefore no

alternation of generations Alternation of generations (also known as metagenesis or heterogenesis) is the predominant type of Biological life cycle, life cycle in plants and algae. It consists of a Multicellular organism, multicellular haploid sexual phase, the gametophy ...

.Fritsch, F.E. (1945). ''The Structure and Reproduction of the Algae''. Vol 2. Cambridge University Press, Cambridge The

thallus Thallus (plural: thalli), from Latinized Greek (), meaning "a green shoot" or "twig", is the vegetative tissue of some organisms in diverse groups such as algae, fungi, some liverworts, lichens, and the Myxogastria. Many of these organisms ...

is a

sporophyte A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase. Life cycle The sporophyte develops from the zygote pr ...

.Smith, G.M. (1938). ''Cryptogamic Botany. Algae and Fungi''. Second edition, Volume ''1'', McGraw-Hill Bok Company, Inc. The

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respectively ...

plants produce male (

antheridia An antheridium is a haploid structure or organ producing and containing male gametes (called ''antherozoids'' or sperm). The plural form is antheridia, and a structure containing one or more antheridia is called an androecium. Androecium is also ...

) and female (

oogonia An oogonium (plural oogonia) is a small diploid cell which, upon maturation, forms a primordial follicle in a female fetus or the female (haploid or diploid) gametangium of certain thallophytes. In the mammalian fetus Oogonia are formed in lar ...

)

gametangia A gametangium (plural: gametangia) is an organ or cell in which gametes are produced that is found in many multicellular protists, algae, fungi, and the gametophytes of plants. In contrast to gametogenesis in animals, a gametangium is a haploi ...

meiosis Meiosis (; , since it is a reductional division) is a special type of cell division of germ cells in sexually-reproducing organisms that produces the gametes, such as sperm or egg cells. It involves two rounds of division that ultimately resu ...

. The

gamete A gamete (; , ultimately ) is a haploid cell that fuses with another haploid cell during fertilization in organisms that reproduce sexually. Gametes are an organism's reproductive cells, also referred to as sex cells. In species that produce t ...

s are released into the surrounding water; after fusion, the

zygote A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicellula ...

settles and begins growth.Flecher, R.L. (1987). ''Seaweeds of the British Isles''. Volume 3, Part 1. British Museum (Natural History), London. Two

taxa In biology, a taxon (back-formation from ''taxonomy''; plural taxa) is a group of one or more populations of an organism or organisms seen by taxonomists to form a unit. Although neither is required, a taxon is usually known by a particular nam ...

, the

corallines 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. The colors of these algae are most typically pink, or some other shade of ...

and

Hildenbrandiaceae 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. The way in which ...

, 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 ''Fucus distichus'' or rockweed is a species of brown alga in the family Fucaceae to be found in the intertidal zones of rocky seashores in the Northern Hemisphere, mostly in rock pools. Description This is a small tufted brown alga. The ...

'', 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

cystocarp A cystocarp is the fruiting structure produced in the red algae after fertilization, especially such a structure having a special protective envelope (as in '' Polysiphonia)''. The structure from which carpospore A carpospore is a diploid spore p ...

ic (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 {{Short pages monitor