Schizoserideae

Belongs within: Delesseriaceae.

The Schizoserideae are delesseriaceous red algae in which carpospores are supported by a candelabra-shaped fusion cell, and growing sections of the thallus have nuclei arranged in a single plane (Hommersand & Fredericq 1997).

Carpospores in chains
Published 24 August 2009
Drachiella spectabilis, one of the few species of Schizoserideae found in the North Atlantic. Note the characteristic iridescence of the fronds. If you look very closely at the photo, you can also see one other characteristic of the family Delesseriaceae to which this species belongs—the fronds are so thin that you can see the features of the rock the alga is growing on through them. Photo by Keith Hiscock.

Despite being the most speciose clade of multicellular marine algae, I must admit I find that the Macrorhodophytina* (multicellular red algae) are not that easy to get a handle on. Most of the significant distinguishing features of various groups of red algae are at the cellular level, and often wrapped up in the eye-wateringly complicated life cycles many macrorhodophytes indulge in. So before I wrote this post, I had to spend a certain amount of time looking up things like just what a “gonimoblast” is. I hope I got it right.

*If you’re wondering why I didn’t use the name Rhodophyta, that’s because Rhodophyta is a larger clade that also includes a few unicellular forms.

The Schizoserideae are a tribe of the red algal family Delesseriaceae containing five genera—Schizoseris, Neuroglossum, Abroteia, Drachiella (Lin et al. 2002) and the recently described Nancythalia (Millar et al. 2002). Delesseriaceae is a large family of red algae with very thin fronds (sometimes only a single cell thick) that may be anything from flat, broad and unbranched to very feathery; however the fronds are not filamentous or polysiphonous (a tubular construstion with a central axial cell surrounded by pericentral cells), distinguishing Delesseriaceae from other families in the order Ceramiales. Ceramiales are in turn distinguished from other red algal orders by the mode of formation of the auxiliary cell. To explain what an auxiliary cell is, I have to tell you that Ceramiales, like many other red algae, alternate between not just two but three distinct generations. As well as having separate multicellular haploid and diploid generations (as also found in many other algae and plants), there is a third stage called the carposporophyte. Mature diploids produce haploid spores that settle and grow into mature male or female haploids. The male haploids release sperm that fertilise the females. However, the resulting zygotes are not released; instead, the diploid nucleus of the zygote abandons the zygote and invades a nearby cell to produce the auxiliary cell (in Ceramiales, the cell that becomes the auxiliary was previously one of the supporting cells for the female gamete). The auxiliary cell then gives rise to a small diploid that remains parasitic on the parent haploid—this is the carposporophyte. The carposporophyte produces diploid spores that grow into new independent diploids.

Mature carposporophyte of Schizoseris condensata, showing the large, branching central fusion cell. Figure from Hommersand & Fredericq (1997).

In members of the Schizoserideae, the female gametangium (the procarp) contains four cells called carpogonia, one of which will get fertilised by the sperm, as well as one or two basal and one or two lateral sterile cells. After the fertilised zygote nucleus has entered the auxiliary cell, the carpogonial cells fuse to form a (wait for it) fusion cell. The auxiliary cell then gives rise to the filaments of the carposporophyte (these are the gonimoblast filaments, in case you were still wondering what that was), which in turn produce the carpospores (diploid spores) in long chains. After forming the carpospore chains, the gonimoblast cells then also fuse with the fusion cell, which ends up being a large, candelabra-shaped supportive structure for the carpospore chains; this candelabra-shaped fusion cell is one of the distinguishing characters for the Schizoserideae* (Hommersand & Fredericq 1997). Other distinguishing features include the lack of protective covering cells on the procarps, and the arrangement of cell nuclei within the fronds—in growing parts of the fronds, all the nuclei line up in a single plane. As well as the morphological characteristics, the tribe has also been supported by molecular analysis (Lin et al. 2001).

*And just to show how much I do for you—those four sentences were the result of probably about an hour of me reading and re-reading the original paper trying to work out just what the heck was going on.

Sections through fronds of Schizoseris condensata, showing the linear arrangement of nuclei. In the bottom section, the alignment is breaking apart in the older part of the frond to the right. Figures from Hommersand & Fredericq (1997).

The main centre of distribution for the Schizoserideae is in the Southern Hemisphere; Abroteia and Nancythalia are both (as far as is known) monotypic and endemic to New Zealand (Millar et al. 2002). The genus Drachiella is the exception, with three of its four species found in the northern Atlantic and the fourth species described only recently from Taiwan and the Philippines (Lin et al. 2002).

Systematics of Schizoserideae

Characters (from Hommersand & Fredericq 1997): Plant body foliose, primarily monostromatic with polystromatic bases, stipes and macroscopic nerves, or tristromatic to polystromatic except at or near margin, and then usually lacking conspicuous nerves. Microscopic veins absent. Growth diffuse, by marginal and intercalary meristems. Nerve and stipe thickenings typically formed by combination of periclinal and anticlinal divisions. Cells containing single parietal chloroplast that is variously lobed, convoluted or ribbonlike, or several chloroplasts present, probably metastable, breaking up and fusing under different conditions. Nuclei 1–many, arranged in a plate across middle of cell in young cells, variously dispersed in mature cells in older tissues. Primary and secondary pit connections conspicuous, median, usually one between each adjacent cell; later-formed secondary pit connections minute, infrequent to abundant at cell surfaces in older parts of blade. Spermatangial sori separate or aggregated on monostromatic or polystromatic portions of blade. Procarps formed singly near margins on either side of thallus, or only on upper surface in some, circular in outline consisting of a supporting cell bearing a large 1–(2-)celled lateral sterile group, a strongly curved 4-celled carpogonial branch in which trichogyne traverses beneath lateral sterile group emerging anterior to it, and small, 1–(2-)celled basal sterile group. Auxiliary cell broader than tall, diploidized by connecting cell and dividing vertically into lateral gonimoblast initial and residual auxiliary cell; gonimoblast filaments at first developing unilaterally in an arc to one side, later radiating in all directions and bearing carposporangia in simple or branched chains; fusion cell extensive, candelabra-like, incorporating sterile groups, cells in floor of cystocarp, and most sterile gonimoblast cells; pericarp 4–6 cell layers thick with ostiole typically off center, overlying first sterile group. Tetrasporangia in small circular sori, or sori confluent; primary tetrasporangia arising from inner cortical cells, usually disposed in two layers surrounded by cortical filaments; secondary tetrasporangia arising from cortical cells and sometimes from central cells. Division of tetrasporangia tetrahedral.

<==Schizoserideae
    |--Polycoryne gardneri Setchell 1923W03, S57
    |--AbroteiaW03
    |    |--A. orbicularis (Harvey) Agardh 1876L27
    |    `--A. suborbicularis [incl. Myriogramme oviformis Kylin 1929]L49
    `--Schizoseris Kylin 1924W03
         |--S. condensata (Reinsch) Ricker 1987 [incl. *S. laciniata Kylin 1924]W03
         |--S. bombayensis (Børgesen) Womersley 2003 (see below for synonymy)W03
         |--S. dichotoma (Hooker & Harvey) Kylin 1924 [incl. Nitophyllum multinerve Hooker & Harvey 1845]W03
         |--S. hymenena (Zanardini) Womersley 2003 (see below for synonymy)W03
         |--S. perriniae (Lucas) Womersley 2003 (see below for synonymy)W03
         `--S. tasmanica Lin & Kraft 1999W03

Schizoseris bombayensis (Børgesen) Womersley 2003 [=Myriogramme bombayensis Børgesen 1931; incl. S. pygmaea Dawson 1950, S. subdichotoma]W03

Schizoseris hymenena (Zanardini) Womersley 2003 [=Nitophyllum hymenena Zanardini 1874; incl. N. gattyanum Agardh 1876, Myriogramme gattyana (Agardh) Kylin 1924]W03

Schizoseris perriniae (Lucas) Womersley 2003 [=Nitophyllum perriniae Lucas 1931, Myriogramme perriniae (Lucas) May 1965]W03

*Type species of generic name indicated

References

Hommersand, M. H., & S. Fredericq. 1997. Characterization of Schizoseris condensata, Schizoserideae trib. nov. (Delesseriaceae, Rhodophyta). Journal of Phycology 33 (3): 475–490.

[L27] Laing, R. M. 1927. A reference list of New Zealand marine algae. Transactions and Proceedings of the New Zealand Institute 57: 126–185.

[L49] Levring, T. 1949. Six new marine algae from New Zealand. Transactions and Proceedings of the Royal Society of New Zealand 77 (3): 394–397.

Lin, S.-M., S. Fredericq & M. H. Hommersand. 2001. Systematics of the Delesseriaceae (Ceramiales, Rhodophyta) based on large subunit rDNA and rbcL sequences, including the Phycodryoideae, subfam. nov. Journal of Phycology 37: 881–899.

Lin, S.-M., J. E. Lewis & S. Fredericq. 2002. Drachiella liaoii sp. nov., a new member of the Schizoserideae (Delesseriaceae, Rhodophyta) from Taiwan and the Philippines. European Journal of Phycology 37: 93–102.

Millar, A. J. K., & W. A. Nelson. 2002. Nancythalia humilis gen. et sp. nov. and Abroteia suborbiculare (Delesseriaceae, Rhodophyta) from New Zealand. Phycologia 41 (3): 245–253.

[S57] Scagel, R. F. 1957. An annotated list of the marine algae of British Columbia and northern Washington (including keys to genera). National Museum of Canada Bulletin 150: 1–289.

[W03] Womersley, H. B. S. 2003. The Marine Benthic Flora of southern Australia. Rhodophytapart IIID. CeramialesDelesseriaceae, Sarcomeniaceae, Rhodomelaceae. Flora of Australia Supplementary Series 18. Australian Biological Resources Study: Canberra, and the State Herbarium of South Australia: Adelaide.

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