OstioleThe pore of the conceptacle. It opens to the outside.
ConceptacleA flask-shaped cavity. The reproductive organs grow inside it.
Conceptacle wallA lining of small cells. The hairs grow from it.
Branched hairsThin branching threads. The antheridia sit on their branches.
AntheridiaSmall oval cells on the branched hairs. They make the sperm.
ReceptacleThe swollen tip of a branch. The conceptacles are sunk in it.
Female conceptacle 4
OogoniumA large oval cell on a short stalk. It holds the eggs.
EggsEight eggs form inside each oogonium.
Stalk cellOne short cell. It joins the oogonium to the wall.
ParaphysesLong unbranched hairs. They carry no reproductive cells.
How this list was compiled: Every name and statement was checked on 2026-10-03 against sources read that day; a name is kept only when two of them use it. (1) Wikipedia, text only: Conceptacle, https://en.wikipedia.org/wiki/Conceptacle (specialized cavities that contain the reproductive organs; situated in the receptacle; open by a small ostiole; antheridia and oogonia; the gametes are let out into the water), and Fucus, https://en.wikipedia.org/wiki/Fucus (conceptacles embedded in receptacles at the tips of the final branches; oogonia and antheridia produce egg cells and sperm that are released into the sea, where fertilization takes place). (2) F. O. Bower and S. H. Vines, A Course of Practical Instruction in Botany, part 2, 1887, public domain, https://archive.org/details/courseofpractica02bowerich (Fucus serratus, pages 47 to 59: the round orifice or ostiole of each conceptacle; male and female conceptacles on different plants; a male conceptacle cut through the ostiole: the spherical or flask-shaped cavity, the ostiole, the hairs that almost fill the cavity and may protrude through the ostiole, the antheridia, single oval cells borne in large numbers on these hairs; the cavity lined by a small-celled tissue from which the hairs arise; thin branched hairs that bear the antheridia, and long hairs, branching less or not at all, that bear none; the female conceptacle: barren hairs, usually unbranched, and oogonia, large oval bodies each seated on a unicellular pedicel, the contents divided into eight parts). (3) George Murray, An Introduction to the Study of Seaweeds, 1895, public domain, https://archive.org/details/cu31924001320930 (the reproductive organs are borne in conceptacles, cavities beneath the surface that communicate with the outside through a narrow opening, the ostiole; the oogonium stands on a pedicel cell, usually very short and sometimes wholly buried in the wall of the conceptacle; eight oospheres in each oogonium, with four, two or one in other genera; the antheridia are the end cells of the branches of much-branched hairs; the paraphyses of the Fucaceae are unbranched, and those near the ostiole frequently protrude). (4) John N. Martin, Botany for Agricultural Students, 1919, public domain, https://archive.org/details/botanyforagricul00mart (rockweeds, pages 321 to 323, figure 278: hollow conceptacles in the swollen tips of the branches, each opening by a pore; in Fucus vesiculosus male and female organs are in separate conceptacles; the oogonium a large, globular, stalked cell with eight eggs; the antheridia oval cells on the side branches of much-branched filaments that project from the wall of the conceptacle; eggs and sperms are discharged from the conceptacle before fertilization). (5) C. Stuart Gager, Fundamentals of Botany, 1916, public domain, https://archive.org/details/fundamentalsofbo00gagerich (sections 212 to 214, on the related rockweed Ascophyllum with notes on Fucus: conceptacles beneath the surface of the swollen tips, opening by short canals; the inner surface covered with hairs, paraphyses; the oogonium attached to the inner surface by a short unicellular stalk; eight eggs in Fucus; figure 174, a female receptacle). Licence: own work
The drawing: Drawn for this site on 2026-10-03 from plain geometry; own work, nothing traced. Licence: own work
How it works
This Fucus male conceptacle labeled diagram is the slide of a botany practical: one flask-shaped cavity in the tip of a rockweed branch, lined with branched hairs that carry antheridia. The second drawing is a female conceptacle with its oogonia.
Read the full guide
The male conceptacle
The cavity opens to the outside through a pore, the ostiole. From its wall grow branched hairs, and on their branches sit many small oval antheridia, which make the sperm.
The female conceptacle
It has the same shape and the same wall. Inside are large oval oogonia, each on a one-celled stalk, with unbranched hairs called paraphyses between them. Each oogonium of Fucus forms eight eggs. Eggs and sperm are shed through the ostiole, and fertilization happens in the sea.
In Fucus vesiculosus and Fucus serratus the male and female conceptacles are on separate plants. Some other species have both organs in one conceptacle.
On a whole rockweed the conceptacles show as small dots on the swollen branch tips.
Questions and answers
What is a conceptacle in Fucus?
A flask-shaped cavity sunk in the swollen tip of a branch, the receptacle. It holds the reproductive organs and opens to the outside through a small pore, the ostiole.
How do you tell a male conceptacle from a female one?
By what is inside. A male conceptacle is filled with branched hairs that carry many small oval antheridia. A female one holds a few large oval oogonia on short stalks, among unbranched hairs.
What is the ostiole of a conceptacle?
The narrow opening at the top. Hairs near it often stick out through it, and the eggs and sperm leave by it.
How many eggs are in a Fucus oogonium?
Eight. The contents of each oogonium divide into eight eggs. Some related seaweeds form fewer.
What are paraphyses?
Hairs that carry no reproductive cells. In Fucus they are long and unbranched, they grow from the conceptacle wall, and those near the ostiole often stick out through it.