Belongs within: Nemaliophycidae.
The Batrachospermales are a group of freshwater red algae characterised by uniaxial gametophytes, together with pit plugs with a domed outer cap layer but no cap membrane (Müller et al. 2002).
Frog spawn multipliers
Published 10 March 2025
When writing previously about red algae on this site, my subject has been of a decidedly marine character. But there are significant lineages of red algae that restrict themselves to fresh water, among which are the representatives of the order Batrachospermales.
Batrachospermales species may most commonly be found growing in moving waters such as streams or springs, where they appear as slender, irregularly branching thalli up to some centimetres in length. The structure of the thalli consists of a single central axis surrounded by distinct whorls of dense lateral branches. These whorls are often embedded in a thick mucilage, resulting in the appearance of a string of gelatinous beads (hence the name of the type genus, Batrachospermum, in reference to its resemblance to frog spawn). Alternately, they may be densely packed to give the overall thallus a cartilaginous consistency (Vis & Necchi 2021). Batrachospermales species commonly grow in slightly acidic waters that may be strongly stained by tannins.
Of course, it wouldn’t be a red alga discussion without having to face some truly ghastly life cycles. Like many red algae, Batrachospermales usually have a triphasic life cycle with independent haploid and diploid generations. The macroscopic form described above is the haploid generation, the gametophyte, which produces the male and female gametes via mitosis. In some species, male reproductive structures (spermatangia) and female reproductive structures (carpogonia) are produced on a single thallus; in others, they are produced separately. After a carpogonium has been fertilised, it grows into a variably sized diploid structure, the carposporophyte, that remains attached to the parent plant. The carposporophyte asexually produces diploid carpospores that are released to settle and germinate into the independent diploid generation.
And this is where things get really complicated. The independent diploid generation of Batrachospermales does not resemble the haploid generation; instead, it grows as a minute filamentous structure. Historically, these filamentous algae were not recognised as related to Batrachospermum, and were described under the genus name Chantransia. ‘Chantransia’ is no longer recognised as a distinct genus but is still used as the label for this growth form. Systematic studies of Batrachospermales tend to focus on the gametophyte generation as chantransia generations are generally uniform and indistinguishable from each other. One study by Necchi & Oliveira (2011) of the genetic relations of two ‘Chantransia’ morphospecies found that whereas one, ‘C. macrospora’, corresponded to a distinct phylogenetic cluster that might represent a single species of Batrachospermales, the other, ‘C. pygmaea’, included samples aligned with a whole range of gametophytes of both the Batrachospermales and the closely related order Thoreales.
Chantransia filaments may reproduce asexually, releasing diploid spores from monosporangia that grow into other chantransia, or they may give rise to the haploid gametophytes. Unlike other red algae, Batrachospermales do not release haploid spores from tetrasporangia. Instead, vegetative meiosis occurs within the chantransia and a haploid gametophyte grows directly from its parent. Whether a given chantransia propagates mitotically or meiotically is influenced by environment, and chantransia populations may persist for extended periods without ever producing gametophytes. One ‘Chantransia pygmaea’ sample from the Hawaiian Islands analysed by Necchi & Oliveira (2011) proved to belong to a species of Thoreales that had never been identified from that part of the world.
One South American species, Acarposporophycos brasiliensis, differs from other Batrachospermales in having a biphasic rather than triphasic life cycle. The carposporophyte generation as found in other species is absent. Instead, fertilised carpogonia give rise directly to the chantransia stage which then grows on the parent gametophyte. No word, as far as I know, on whether this piggy-backing chantransia can then itself give rise in place to a daughter gametophyte, and so on and so on, to produce a literal chain of generations.
Systematics of Batrachospermales
Batrachospermales
| i. s.: Tuomeya americanaMS02
| Paralemanea catenataMS02
| Nothocladus nodosusMS02
| ‘Audouinella’ macrosporaMS02
|--Lemanea [Lemaneaceae, Lemaneae]HS02
| |--L. fluriatilis [=Sacheria fluriatilis]G03
| `--L. torulosaG64
`--BatrachospermaceaeHB03
|--Psilosiphon scopariumHB03
|--SirodotiaHS02
| |--S. huillensisMS02
| `--S. suecicaMS02
`--BatrachospermumMS02
|--B. alpestreG64
|--B. atrumMS02
|--B. bombusinumG64
|--B. boryanumMS02
|--B. gelatinosumMS02 [incl. B. confusumG64]
|--B. helminthosumMS02
|--B. louisianaeMS02
|--B. macrosporumMS02
|--B. moniliformeG64
|--B. proliferumG64
|--B. pulcherrimumG64
|--B. rubrumG64
|--B. stagnaleG64
|--B. turfosumMS02
|--B. vagumG64
`--B. virgatodecaisneanumMS02
*Type species of generic name indicated
References
[G03] Gnilovskaya, M. B. 2003. The oldest tissue differentiation in Precambrian (Vendian) algae. Paleontologicheskii Zhurnal 2003 (2): 92–98 (translated: Paleontological Journal 37 (2): 196–204).
[G64] Gray, J. E. 1864. Handbook of British Water-weeds or Algae. R. Hardwicke: London.
[HS02] Harper, J. T., & G. W. Saunders. 2002. A re-classification of the Acrochaetiales based on molecular and morphological data, and establishment of the Colaconematales ord. nov. (Florideophyceae, Rhodophyta). European Journal of Phycology 37: 463–476.
[HB03] Harvey, A. S., S. T. Broadwater, W. J. Woelkerling & P. J. Mitrovski. 2003. Choreonema (Coralllinales, Rhodophyta): 18S rDNA phylogeny and resurrection of the Hapalidiaceae for the subfamilies Choreonematoideae, Austrolithoideae, and Melobesioideae. Journal of Phycology 39: 988–998.
[MS02] Müller, K. M., A. R. Sherwood, C. M. Pueschel, R. R. Gutell & R. G. Sheath. 2002. A proposal for a new red algal order, the Thoreales. Journal of Phycology 38: 807–820.
Necchi, O., Jr, & M. C. Oliveira. 2011. Phylogenetic affinities of “Chantransia” stages in members of the Batrachospermales and Thoreales (Rhodophyta). Journal of Phycology 47: 680–686.
Vis, M. L., & O. Necchi Jr. 2021. Freshwater Red Algae: Phylogeny, taxonomy and biogeography. Springer.