Plants range from 2-30 cm in height and can occur as feathery tufts (Featured image above) owing to the free filaments or form weak rope-like strands (Image A). Branching is typically opposite or unilateral (Image B) with vegetative cells 20-45 µm wide by 20-50 µm long, the cells ranging from squat through square to rectangular in different regions of the filaments and characterized by discoid plastids (Image C). Filaments are typically uniseriate, rarely biseriate, this typically associated with older cells bearing the paired opposite branches. In basal to mid thallus regions the branch tips tend to become tendril-like and contribute to the development of the rope-like habit (Image D). Although details were difficult to discern in the rehydrated material, at times only the basal cell or two appeared as normal vegetative cells before the transition into the rambling hair-like filaments. Unilocular structures are intercalary, but can develop within a few cells of the tip, and typically develop as series of 30+ locules extending to and through branching points. Individual locules square to rectangular 20-37 µm wide by 22-40 µm long reaching the larger dimensions with maturity (Image E). Unilocular sporangia can also be biseriate (Image F). Plurilocular structures are similarly intercalary, although they may be terminated by a long hair-like filament, and develop as concatenated (separated by a few vegetative cells) series with each cluster of contiguous structures typically containing 10-20 locules (Image G).
This species is relatively rare, but nonetheless widespread in our eastern flora extending from RI to Churchill, MB. Specimens were collected in upper pools extending through the intertidal to slightly subtidal (4 m), and were typically on fucoids (notably Ascophyllum nodosum (Linnaeus) Le Jolis), but also on other algae and occasionally hard substrata (eg. cobble, mussels). In our flora confusion with the more common Pylaiella washingtoniensis Jao is possible, but that species has a stronger tendency to be rope-like in habit, has opposite branches characterized by a leading and lagging branch, and distinctive descending rhizoids in contrast to the modified branch apices in Pylaiella littoralis. Furthermore, the number of contiguous segments converted to reproductive structures seems limited to fewer than 12 in Pylaiella washingtoniensis Jao while in Pylaiella littoralis they routinely exceed 15-20 in a plurilocular series and 30 in a unilocular series. Pylaiella varia Kjellman is more restricted in its habitat (salt marsh and sheltered estuaries) and rarely exhibits opposite branching with its unilateral branches formed at ~90o to the bearing axis. Confident identification requires molecular tools.
Image A. Typical collection from the lower mid intertidal on Ascophyllum nodosum (Linnaeus) Le Jolis. Note the rope-like strands in the central portions of the thallus despite the overall fluffy appearance (Halls Harbour, Bay of Fundy, NS; GWS012401).
Image C. Closeup of vegetative cells displaying the discoid plastids (GWS045110).
Image D. Rhizoid-like extensions of branch tips in older portions of thalli contribute to the rope-like habit (aniline stained rehydrated material) (mid intertidal pool on Ascophyllum nodosum (Linnaeus) Le Jolis, Starboard, ME; GWS003634).
Image E. Long contiguous stretch of intercalary unilocular structures (GWS045110).
Image F. Biseriate development of unilocular structures (GWS045110).
Image G. Intercalary plurilocular structures (aniline stained rehydrated material) (low intertidal pool on Fucus distichus Linnaeus, Gordon Pt., Churchill, MB; GWS005318).