𝘓𝘪𝘤𝘩𝘦𝘯𝘰𝘮𝘱𝘩𝘢𝘭𝘪𝘢: Trials of a Basidiolichen

Fruiting bodies of (A) Lichenomphalia hudsoniana (H. S. Jenn.) Redhead, Lutzoni, Moncalvo & Vilgalys, (B) L. umbellifera (L.) Redhead, Lutzoni, Moncalvo & Vilgalys, and (C) L. velutina (Quél.) Redhead, Lutzoni, Moncalvo & Vilgalys. Figures from Liu et al. (2018).

 Lichens are very weird. Undeniably ubiquitous, they encrust just about every surface that will let them (Asplund & Wardle (2016) claim as much as 8% of the Earth's surface is covered in lichens!). So common are these things that they remain chronically overlooked and understudied. Lichens are the quintessential symbiotic relationship, a composite organism comprising unicellular algae (or sometimes cyanobacteria), referred to as the "photobiont," living intertwined with the hyphal strands of a fungus. The relationship is nearly inseparable and lichens are truly their own type of organism distinct from their component parts. Taxonomically, lichens are named according to the fungal component and they most certainly do not form a monophyletic group. Many different lineages of fungi have "lichenized" throughout Earth's history, lending to the abundance and diversity of these composites. However, most lichens are derived from ascomycete fungi. Lichenization is much less common among the Basidiomycota, the large phylum of fungi that includes the most familiar mushroom-forming lineages. Liu et al. (2018) refer to 172 described basidiolichens, which themselves have evolved convergently across five orders. 

Figures showing the types of thalli exhibited by Lichenomphalia from Liu et al. (2018). (D) Globular "Botrydina"-type. (E) Sqamulose "Coriscium"-type.

The subjects of this post are Lichenomphalia, fifteen (likely more) species of basidiolichens in the family Hygrophoraceae. These lichens are widely distributed in temperate to arctic and alpine regions of the Northern Hemisphere as well as disjunct populations in Australia and Chile. The lichen identity of these fungi is a relatively recent revelation; the typical mushroom fruiting bodies and asexual thalli of these species were described as separate, unrelated organisms dating back to Linnaeus (1753).  Two of these former genera, "Botrydina" and "Coriscium," are still used to refer to different types of thalli produced by these lichens. "Botrydina" are globular, while "Coriscium" are "squamulose" (referring to the flat, scaly texture of many common lichens). 

Ecologically speaking, Lichenomphalia are fairly typical basidiomycetes, growing in damp, mossy places and often leaching nutrients from decaying wood. They are also common in harsh environments, such as the windy tundras of Greenland and Nunavut. The photobionts of Lichenomphalia are members of the globally distributed algae genus Coccomyxa, which contribute to the vibrantly green thallus of some species. These lichens were formerly placed in the tricholomatacean genus Omphalina; their status as a monophyletic radiation of lichenized agarics was determined via a phylogenetic analysis by Redhead et al. (2002), establishing the genus Lichenomphalia. Lichen and fungi in general are among the most common organisms on Earth with untold importance to global ecosystems, yet taking the time to research any single lineage only reveals how little we actually understand about our fungal neighbors. 

Lichenomphalia hudsoniana (H. S. Jenn.) Redhead, Lutzoni, Moncalvo & Vilgalys. Notice the contrast between the yellow fruiting body and green thallus, it's no surprise they were considered separate organisms for hundreds of years. Photo by Troy McMullin from here.

REFERENCES

Liu, D., Goffinet, B., Wang, X. Y., Hur, J. S., Shi, H. X., Zhang, Y. Y., ... & Wang, L. S. (2018). Another lineage of basidiolichen in China, the genera Dictyonema and Lichenomphalia (Agaricales: Hygrophoraceae). Mycosystema, 37(7), 849-864.

Moncalvo, J. M., Vilgalys, R., Redhead, S. A., Johnson, J. E., James, T. Y., Aime, M. C., ... & Miller Jr, O. K. (2002). One hundred and seventeen clades of euagarics. Molecular phylogenetics and evolution, 23(3), 357-400.

Adventures in 𝘉𝘦𝘨𝘰𝘯𝘪𝘢: Section 𝘗𝘳𝘪𝘵𝘻𝘦𝘭𝘪𝘢

Begonia paranaensis Brade, a species endemic to Brazil's Atlantic Forest. Photo copyright Mauro Peixoto.

 

I'm a little obsessed with begonias, but their near universal popularity with gardeners around the world suggests I'm not alone. Begonia is one of the largest and most diverse genera of any organisms, containing anywhere from 1800 to over 2,000 species depending on who you ask and many hundreds more cultivated varieties and hybrids. I plan to devote multiple articles to this beast of a taxonomic group but our adventures in Begonia begin with the section Pritzelia. A rather enigmatic group of begonias restricted to South America, the primary center of diversity for these plants is the Atlantic Forest of eastern Brazil. Doorenbos, Sosef & Wilde (1998) assigned 122 species to Pritzelia, but new species have been described in the years since. Exactly what defines a Begonia as a Pritzelia is tough to nail down. They are diverse in leaf and floral anatomy and exhibit a range of growth habits from rhizomatous creepers to shrubs and trees. The two universal features uniting Pritzelia species (according to Doorenbos, Sosef & Wilde, 1998) are placental anatomy and the presence of cystoliths in the leaf cells, despite the fact that cystoliths are not present in at least two species.

Anatomical diagram of Begonia epipsila Brade showing "typical" features of sect. Pritzelia, from Doorenbos, Sosef & Wilde (1998).

Technicalities aside, what does it mean to live life as a Pritzelia? Like most begonias, these plants are often highly endemic residents of shady tropical understories. However, as mentioned earlier, this section breaks the typical Begonia mold with the evolution of tree-like species. Among these is the remarkable B. arborescens Raddi. Referenced as one of the largest free-standing begonias (Tebbitt 2005), I cannot for the life of me find any actual size references. It is safe to assume that these are relatively small trees, standing in the humid shade of the tall canopy trees. Nonetheless, these are fascinating plants that resemble elms Ulmus spp. more than begonias. It has even been suggested that B. arborescens may mimic species of Cecropia, a large genus of tropical trees protected from herbivores by a symbiotic relationship with ants (Tebbitt 2005). 

The oddly elm-like leaves of Begonia arborescens Raddi. Photo copyright Arthur Couto from here.

Pritzelia are not commonly cultivated compared to other begonia sections, with the notable exception of B. coccinea Hook. This shrubby species (also endemic to the Atlantic Forest) has been widely hybridized to create a suite of cultivars known collectively by gardeners as "angel wing" or "cane" begonias. Deducing the actual ancestry of many domestic cultivars is nearly impossible; the world of begonia cultivation can feel mysterious and intimidating for those uninitiated. It is worth pointing out that many wild begonia species exhibit "angel wing"-like leaves and cane-like growth habits. Indeed, many members of this genus have evolved forms and patterns naturally that rival our artificially bred cultivars in their extravagance.

Begonia "Benigo Pink," one of the many "angel wing" cultivars with B. coccinea ancestry. Photo from here.

Flowers of a wild-type Begonia coccinea, from here.

REFERENCES

Doorenbos, J., Sosef, M. S. M., & De Wilde, J. J. F. E. (1998). The sections of Begonia including descriptions, keys and species lists (Studies in Begoniaceae VI) (No. 98-2). Wageningen Agricultural University.

Tebbitt, M. C. (2005). Begonias: cultivation, identification, and natural history. Timber Press (OR).

Snails Adrift: 𝘙𝘦𝘤𝘭𝘶𝘻𝘪𝘢 and 𝘑𝘢𝘯𝘵𝘩𝘪𝘯𝘢

 

Adult pair of Recluzia johnii (Holten, 1802) with eggs and bubble raft. (Photo copyright Denis Riek from here)

   Earth's oceans are incredibly vast and inhabited by nearly uncountable scores of organisms, yet the surface of the ocean itself is one of the emptiest habitats there is. The sea/sky interface is home to a tiny yet fascinating suite of organisms known collectively as the "pleuston" (alternatively "neuston"), most notably including multiple families of floating cnidarians, mats of floating macroalgae in the genus Sargassum, and even a genus of sea-skating insects (Halobates). A remarkable group of gastropods fill the niche of drifting predators: the genera Janthina and Recluzia. These gastropods belong to the Epitoniidae, a family of obligate cnidarian predators and parasites known by shell collectors as "wentletraps." Janthina are prolific predators of pleustonic hydrozoans such as the infamous man o' war Physalia physalis (Linnaeus, 1758) and unusual by-the-wind sailor Velella velella (Linnaeus, 1758). Recluzia are more specialized, feeding on the strange free floating anemones of the Minyadidae. There are eight valid species of Janthina currently recognized (three are extinct) and two species of Recluzia. The genera are easily distinguished even as empty shells by color alone. Recluzia shells are a cream/yellow color similar to many benthic epitoniids, but Janthina shells are uniquely purple/violet, often considered a camouflage adaptation to an existence shrouded in constant blue.

Indeed, life adrift has come with a range of interesting adaptations. These snails cannot swim on their own (at least not as adults); their individual survival is contingent on them remaining permanently attached to a floating raft they construct from rigid bubbles. The bubbles are made by cupping the anterior portion of the snail's "foot" above the waterline and coating the air bubble in mucus, which hardens immediately on contact with sea water. This same mucus binds the foot of the snail to the raft. Losing grip on their raft means certain death as the animal helplessly sinks into the deep. Maintaining a grip also prevents these gastropods from hiding within their shells, a basic defense strategy for most snails. A lack of body mobility has acted as selection pressure for the evolution of an enlarged and highly mobile head in Janthina. Recluzia are not so highly derived anatomically, resembling benthic epitoniids to a much higher degree than Janthina with a more elongate shell and small head.

Figures showing the modified head and general habitus of Janthina janthina (Linnaeus, 1758) from Beu (2017).

Janthina and Recluzia are so divergent from the rest of the Epitoniidae that their taxonomic affinities were mostly contentious until the early 2010s. Churchill et al. (2011) found both genera to be nested firmly within the epitoniids, dissolving the formerly recognized "Janthinidae." Despite extremely similar lifestyles, it has been suggested that these two genera may not even form a monophyletic group with each other. Beu (2017) carried out the most detailed revision of this group to date and concluded that Janthina and Recluzia took to the surface independently, surely representing one of the most remarkable examples of convergent evolution yet known. Recluzia seems to have adapted to the pleuston much more recently than Janthina as evidenced by a lack of fossil record and significantly fewer anatomical specializations. Janthina possess a fossil record dating back to the Miocene and are generally much better studied and seemingly much more common than Recluzia. Still very much unknown is what the transition from the sea floor to the sea surface looked like. Only time will tell what other secrets these fascinating mollusks are hiding.

Shells of all recognized extant species of Janthina and Recluzia from Beu (2017). 

REFERENCES

Beu, A. G. (2017). Evolution of Janthina and Recluzia (Mollusca: Gastropoda: Epitoniidae). Australian Museum.