Palisada, IN

Popolizio, Thea R., Schneider, Craig W., Jongbloed, Walter M., Saunders, Gary W. & Lane, Christopher E., 2022, Molecular analysis resolves the taxonomy of the Laurencia complex (Rhodomelaceae, Ceramiales) in Bermuda and uncovers novel species of Chondrophycus and Laurenciella, Cryptogamie, Algologie 20 (1), pp. 1-30 : 15-16

THE GENUS PALISADA IN BERMUDA

The molecular sequence data we have produced verify that Palisada perforata in Bermuda is conspecific with specimens from the type locality (Canary Islands, Spain) with 0.6% and 0.2% intraspecific divergence in COI-5P and rbc L, respectively. This species is the most common member of the genus Palisada in our Laurencia complex collections, and is predominantly intertidal with a few exceptions from shallow subtidal sites in the Florida Keys and a single subtidal collection from a shallow subtidal site (3-4 m) off Bermuda’s north shore. Another species in the genus, P. flagellifera , with a type locality in the Indian Ocean, is reported as pantropical with amphi-Atlantic reports from Cuba ( Areces et al. 2003), Brazil ( Fujii et al. 2006) and the Canary Islands ( Gil-Rodriguez et al. 2010). Our COI-5P barcode investigation indicated a group within the Palisada clade that was distinct from reported Bermuda species – rbc L sequences from these collections align with P. flagellifera sequences from Brazil and the Canary Islands (intraspecific divergence = 0.2%). Comparative molecular data are not available for specimens from the Indian Ocean type locality. The present report represents the first record of P. flagellifera in Bermuda.

Accounts of Palisada corallopsis (as Laurencia corallopsis ) (Montagne) M.Howe in Bermuda (type locality = Cuba) have appeared in the literature since the early 20th century [ Howe 1918, as L. corallopsis ; Frederick 1963, as L. corallopsis ; Schneider 2003, as Chondrophycus corallopsis (Montagne) K.W.Nam ]. Harvey’s (1853) L. cervicornis Harvey (type locality

= Key West) had long been merged with P. corallopsis ( Howe 1918) and Collins et al. (1917, P.B.-A. no. 2187) and Collins & Hervey (1917) reported their collections from Bermuda as L. cervicornis Harvey ( Schneider 2003) . Littler & Littler (2000: 490, as L. cervicornis ) argued that P. cervicornis was smaller in habit with smaller surface cells than P. corallopsis and therefore distinct from the latter, a position accepted by Dawes & Mathieson (2008). More recently, specimens of P. cervicornis and P. corallopsis collected from the Florida Keys were included in a phylogenetic analysis that supported these species as unique ( Collado-Vides et al. 2017).

Specimens field-identified as Palisada corallopsis from Bermuda and the Florida Keys are genetically variable in both COI-5P and rbc L analyses. For the latter gene, one genetic entity from Bermuda is closely related (0.6% divergence) to a specimen from Caribbean Mexico likewise identified as P. corallopsis , and considered to be representative of the species due to its proximity to the type locality ( Cuba). Collado-Vides et al. (2017) published an rbc L sequence of P. corallopis from material collected in Florida that differed by 0.4% from the Caribbean Mexico specimen sequence, similar to the genetic divergence seen between the latter and Bermuda specimens. The other genetic entity from Bermuda previously identified as P. corallopsis aligns instead with specimens of P. cervicornis also reported by Collado-Vides et al. (2017) with 0.9% divergence in rbc L between the sequences. A third undescribed species that we collected in the Florida Keys is sister to P. cervicornis from Bermuda and Florida (2.0% divergence in rbc L, Table 1).

Our collections grouping with Caribbean specimens identified as Palisada corallopis cannot be distinguished from Montagne’s (1842) protologue of Sphaerococcus corallopsis Montagne (now P. corallopsis ) from Havana, Cuba. Our specimens grouping with L. cervicornis from Florida are morphologically indistinguishable from the Collins et al. (1917) Bermuda specimens in P.B.-A. (no. 2187), except for the presence of uniform medullary cell wall thickenings in the recently collected Bermuda specimens. These were not found when examining Collins’ specimens. However, both are in accordance with the original description of L. cervicornis provided by Harvey (1853). Without genetic sequencing, we have opted to leave P.B.-A. (no. 2187) under this name as Harvey called it, with the assumption that cell wall thickening is a variable trait.

The absence of lenticular thickenings is also observed when comparing recent Bermuda collections of Palisada cervicornis and P. corallopis , the latter species lacking this character. Palisada cervicornis specimens from Bermuda have thinner main axes, though this may simply be a result of younger age. In Bermuda specimens, surface cell diameters are also marginally smaller in P. cervicornis (18-30 µm) compared to P. corallopsis (23-45 µm), in line with the observations for Caribbean isolates ( Littler & Littler 2000). Other Palisada specimens in this clade collected in Key West are morphologically distinct from the two Bermuda species as well as P. cervicornis specimens described by Collado-Vides et al. (2017) from Florida ( Table 4). Further study is required to determine whether the Key West collections represent a known or novel species of Palisada .

Palisada furcata from Brazil also groups in the P. corallopsis clade, with 1.8% divergence from its closest congener, P. corallopsis from Mexico. But there are 14 ambiguities in the P.furcata sequence, so that distance estimate is likely to change with better quality sequence data. While the phylogenetic relationship of P. furcata to P. corallopsis is unresolved in our analysis ( Fig. 1), the close grouping warrants comparing the morphological characters for these species ( Table 4). Palisada furcata can be distinguished from P. corallopsis morphologically by its larger overall habit, cylindrical to slightly flattened (vs. swollen) branchlet tips, and smaller outer cortical cells. Unfortunately, we did not collect fertile P. corallopsis to compare tetrasporangia, a character that has not been described for this species in previous publications.