Gallaicolichen, a new genus of foliicolous lichen with unique diaspores




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Festschrift in Honour of David Galloway.

 : Bibliotheca Lichenologica

J. Cramer in der Gebrüder Borntraeger Verlagsbuchhandlung, Berlin, 2006.

Gallaicolichen, a new genus of foliicolous lichen with unique diaspores

Emmanuël SÉRUSIAUX1 and Robert LÜCKING2

1 Plant Taxonomy & Conservation Biology Unit, University of Liège, Sart Tilman B22, B-4000 Liège, Belgium. e-mail:E.Serusiaux@ulg.ac.be


2 Department of Botany, Field Museum, 1400 South Lake Shore Drive, Chicago IL-60605-2496, USA. e-mail: rlucking@fieldmuseum.org
Abstract : The new genus and species Gallaicolichen pacificus Sérus. & Lücking is described. Goniocystangia-like structures are formed with unique diaspores and we introduce the new terms peltidiangium (pl.: peltidiangia) and peltidium (pl.: peltidia) for them. Those diaspores are disc-like structures with a regular pattern of organization, made of small arms of dichotomously branched cells of Phycopeltis, all linked up to a central foot and coiled up inwards, and including a tiny, regularly arranged layer of mycobiont cells. Ascomata and conidiomata are unknown and the taxonomic position of this new genus cannot be determined. It grows on living leaves in Hawaii (type material), Australia/Queensland, New Caledonia and Vanuatu.
Keywords : Hawaii, Australia, Queensland, New Caledonia, Vanuatu, goniocystangia, goniocysts, peltidiangia, peltidia
Introduction
At the symposium dedicated to foliicolous cryptogams in Eger (Hungary) in 1995, our colleague and friend Dr. Clifford Smith gave us a collection of a fascinating foliicolous lichen he had just gathered in Hawaii. It produces basket-like goniocystangia and we first tought it could represent a further species of foliicolous Opegrapha with goniocystangia, a group of six related species (Sérusiaux 1985, Aptroot et al. 1997: 119-120, Lücking 2006). Detailed examination however showed that the “goniocysts” produced are very unusual and represent a different structure. Several other gatherings have been made in Queensland/Australia, New Caledonia and Vanuatu, but no fertile material could be detected. Although we have no data to support a sound taxonomical position, we are convinced that this lichen is not congeneric with any of the known foliicolous lichen genera and hence we describe a new genus and species for this taxon.
Material and Methods
The material was examined in distilled water, in lactophenol cotton-blue (LCB) and in Lugol solution. All measurements refer to water mounts. Air-dried herbarium material for the study by SEM was mounted on polished aluminium stubs using a transparent two-component epoxy glue, gold-coated in a Balzers Union SCD 040 sputter and examined with a Cambridge Stereoscan S 200 scanning electron microscope.
Gallaicolichen pacificus Sérus. & Lücking gen. & sp. nov. Fig. 1-12
Genus et species nova lichenum foliicolum, thallo crustaceo, alga ad Phycopeltem pertinens. Thallus peltidiangiis instructus, ad « goniocystangiis » Opegrapharum similibus, sed peltidiis disciformibus hyphis fungorum in strato algarum inclusis differt. Ascomata et conidiomata non visa.
Type: USA, HAWAIIAN Is, Hawaii, Hamakua, Kolukola Park, on leaves of Syzygium cuminii, 11 July 1995, C. W. Smith s. n. (LG—holotypus).
= Genus sp. (goniocytangia) in Lücking & Kalb (2001: 257).

= Gen. nov. et spec. nov. in Lücking et al. (2001: 207).


Thallus foliicolous, epiphyllous, composed of rounded patches, 0.5-1.2(-1.7) mm in diam., pale greenish yellow to pale yellowish gray, or very pale yellowish, with a slightly lobulate margin, surface somewhat shiny, smooth or very slightly uneven (under high magnification), coalescing when contiguous, up to 20 µm thick, formed of a loose network of interwoven hyphae and large, regular plates of photobiont cells, containing large (up to c. 25 x 10 µm) oxalate crystals, mostly present in mature parts and absent near the margins; cortex sometimes developed, sometimes completely absent, formed of a single layer of parallepipedic or polygonal cells, sometimes with a slightly brownish wall, 5-7 x 2-3 µm; prothallus usually present, membranaceous and colourless, rarely bluish or brownish. Photobiont: a species of Phycopeltis (Trentepohliaceae) with greenish brown, c. 8-10(-11) x 4-5 µm cells, regularly and radiately arranged rows in plates. Goniocystangia-like structures always present (here named peltidiangia), 1-5(-8) per thallus patch, the first one developing at the center, almost perfectly circular, 0.1-0.15(-0.2) mm in diam. and c. 0.13-0.15 mm high, formed by a rather thick erect margin with its inner part typically whitish and made of raised, not agglutinated hyphae and its outer part usually covered by the thallus. Diaspores (here named peltidia) numerous, usually filling up the peltidiangia cavity, disc-like, c. 25-55 µm in diam. and c. 10-15 µm thick, with a regular pattern of organization: small arms of dichotomously branched (1-2 branching points) cells of Phycopeltis, all linked to a central foot-like structure and coiled up inwards on the other side where they encompass a tiny, regularly arranged layer of mycobiont cells; 1-2 extremities of hyphal filaments usually present between algal arms and easily seen on the diaspores outer surface; extremities of algal arms slightly but distinctly inflated, and refringent. Ascomata and conidiomata not observed.
Etymology : We wished to name this new genus after our most distinguished friend and colleague, Dr. David J. Galloway for his outstanding contribution to lichens taxonomy and ecogeography, especially in the Southern Hemisphere. We looked up for the meaning of the name Galloway and came up with « foreign Gael ». The Gaels are an ethno-linguistic group in Ireland, Scotland and the Isle of Man, speaking one of the Gaelic languages and presumably originating from Gallaecia, a Roman province in the NW of the Iberic peninsula. The province name was given by the Romans after the tribe of the « Gallaicoi », and we used this name to form that of our new genus.

Notes: Based on corticolous collections from Rwanda and Uganda (East Africa), Sérusiaux et al. (2006) described the new genus and species Nyungwea pallida, characterized by a thin thallus lichenized with Trentepohlia and short, erect, brush-like stipes producing goniocysts along most of their length. They review the current use of the term “goniocyst” and highlight the different types of diaspores described by this term. In all cases mentioned, it is clear that a goniocyst is made of a single or several algal cells embedded by fungal hyphae, remaining as distinct filaments surrounding the algal cells or forming a typical paraplectenchymatous envelope. Upon a rapid examination of the taxon dealt with in this paper and especially because of its apperance being similar to that of the Opegrapha lambinonii group, one could be proned to include the diaspores produced into the rather large concept of goniocysts currently in use.

Yet this option cannot be followed for our new genus and species Gallaicolichen pacificus. Indeed, the photobiont Phycopeltis forms tiny diaspores that look like “clenched fists” locking up, in “the hand palm” so developed, an apparently single layer of mycobiont cells, forming a regular “tiled floor”. This set of mycobiont cells, arranged in the “hollow of the hand” formed by the photobiont cells, is best seen when the diaspores are hydrated and examined with a photonic microscope. Furthermore, and this feature is best seen with the SEM microscope and dry diaspores, the mycobiont hyphae manage to creep in between the photobiont cells in a very regular pattern. By all means, the respective position of the two partners forming those diaspores is the reverse of that observed in the goniocysts as surveyed by Sérusiaux et al. (2006): here the mycobiont cells are embedded, or almost so, by algal cells. Early stages of the development of those diaspores can be seen through examination of gently squashed thalli with the photonic microscope: observations are not easy as the thallus is filled with oxalate crystals, but nevertheless, rounded sets of a few (6-14) algal cells can be seen to form regularly dichotomous, parallel or slightly diverging lobes (or arms) at their periphery; the dichotomous branching can occur once or twice. These are the primordia of the diaspores produced in the goniocystangia-like structures. The central cells, not forming peripheral digitations, will eventually form the “foot” of the diaspore, while the digitations will eventually close up and form the “clenched fists” around the mycobiont “tiled floor”.


The diaspore primordia develop upon the initiative of the algae and show the branching pattern that has been observed by Sanders & Lücking (2002) in their study of reproduction strategies and thallus development in leaf-dwelling lichen communities : young thalli lichenized with Phycopeltis show dichotomous, parallel or slightly divergent branching at the periphery. Such observations are consistent with the morphological and development data provided by Thompson & Wujek (1997: 68) for non-lichenized Phycopeltis : « In those species characteristically producing a disk of radiating elements, the apical cells regularly bifurcate and a system of equally dichotomous filaments is produced ». We are therefore convinced that the algal cells are the driving force of the development and structure of the diaspores produced by the lichen taxon dealt with here, and the thus formed propagules closely resemble a Phycopeltis primordium, with the only difference that they enclose fungal hyphae to ensure simultaneous dispersal of both bionts.

To our knowledge, this feature is unique in diaspores containing the photobiont and the mycobiont of lichenized fungi: the photobiont partner organizes the diaspore and envelops (or almost so) its mycobiont partner. The regular organization pattern of those diaspores is also a unique feature. Furthermore, it is remarkable that the algal cells produce an intracellular, dense, refringent compound at their tips, which we interpret as a means of strengthening or floating during dispersal, or both.

Although a clarification of the structure and ontogeny of soredia and goniocysts is urgently needed, we introduce the new term “peltidium (pl.: peltidia)” to describe such diaspores as they are clearly distinct; we further suggest to use “peltidiangium (pl.: peltidiangia)” to designate the basket-like structures in which they are produced. The name is derived from the algal genus name Phycopeltis.


We cannot make any sound suggestions on the taxonomic position of our new taxon with the current data available, because no ascomata nor conidiomata could be found. The general appearance of the thallus can point to very different groups, such as the Arthoniaceae, Porinaceae or Roccellaceae (Mazosia or Opegrapha). If ascomata cannot be detected, the production of DNA sequences is needed to assess its taxonomical relationships.

Ecology and distribution : Gallaicolichen pacificus is a foliicolous lichen so far found only in the Pacific Ocean area, especially on its S-E side: it has been collected in the Hawaii archipelago, the Vanuatu archipelago, Queensland in Australia, and New Caledonia. Quite surprizingly, it has not been detected in Papua New Guinea, a country in the same area where extensive collections of foliicolous lichens have been made.

Additional specimens : Australia. Queensland, Moses Creek, 35 km SSE of Cooktown, 15°47’S 145°17’E, 240 m, 1995, H. Streimann 57612A (CANB). — New Caledonia. Province Sud, Monts Koghis-Dumbéa, 15 km NNE of Nouméa, 22°14’S 166°30’E, 550 m, tropical rainforest with Cryptocarya macrocarpan, Bureavella wakere, Hernandia cordigera, Cyathea intermedia, 23 Aug. 1994, K. & A. Kalb s .n. (hb Kalb, LG). — VANUATU: Espiritu Santo, Mt. Malel, Oct. 1998, J. Streimann & Ala s. n. (F).
Acknowledgments

We thank very warmly our colleague and friend Dr. Clifford Smith for having made available his collection of this fascinating species in 1995. Dr. Klaus Kalb also made his material from New Caledonia available for this study, as well as the curators of CANB and F for material from Australia and Vanuatu. We also thank the staff of the University of Liège in charge of the SEM equipment, the so-called Catµ, and especially Dr. Ph. Compère, for their help and assistance in the preparation of the material.


References

Aptroot, A., Diederich, P., Sérusiaux, E. & Sipman, & H. J. M. (2001) : Lichens and Lichenicolous Fungi from New Guinea. Bibliotheca Lichenologica 64: 1-220.

Lücking, R. (2006) : Foliicolous lichenized fungi. Flora Neotropica (in press).

Lücking, R. & Kalb, K. (2001) : New Caledonia, foliicolous lichens and island biogeography. Bibliotheca Lichenologica 78: 247-273.

Lücking, R., Streimann, H. & Elix, J. A. (2001) : Further records of foliicolous lichens and lichenicolous fungi from Australasia, with an updated checklist for continental Australia. The Lichenologist 33: 195-210.

Sanders, W. B. & Lücking, R. (2002) : Reproductive strategies, relichenization and thallus development observed in situ in leaf-dwelling communities. New Phytologist 155 : 425-435.

Sérusiaux, E. (1985) : Goniocysts, goniocystangia and Opegrapha lambinonii and related species. The Lichenologist 17: 1-25.

Sérusiaux, E., Fischer, E. & Killmann, D. (2006) : Nyungwea, a new genus of lichen with goniocysts-producing stipes from Rwanda and Uganda (East Africa). The Lichenologist 38 : 115-121.

Thompson, R. H. & Wujek, D. E. (1997) : Trentepohliales : Cephaleuros, Phycopeltis and Stomatochroon. Morphology, Taxonomy, and Ecology. Sciences Publishers Inc., Enflield.

Captions for figures
Fig. 1-6. Gallaicolichen pacificus (type collection, Hawaiian Is.). 1. General habit, with several thalli and their peltidiangia (bar = 1 mm). 2-5. Peltidia mounted in water. 2. Three peltidia with slightly inflated refringent tips of the Phycopeltis cells (bar = 20 µm). 3. Peltidium with the regularly arranged mycobiont cells surrounded by Phycopeltis cells (bar = 15 µm). 4-5. Primordia of the peltidia formed by Phycopeltis and showing a few, polygonal cells in the center, surrounded by dichtomously branched cells starting to produce a dense and refringent compound (bar = 10 µm).

Fig.6-8. Gallaicolichen pacificus (type collection, Hawaiian Is.) (bars= 10 µm). 6. Lateral view of a young peltidiangium with its inner margin made of raised, not agglutinated hyphae. 7. Upper view of a mature peltidiangium with numerous peltidia. 8. Detailed view of the inner margin of a mature peltidiangium cavity.

Fig. 9-12. Gallaicolichen pacificus (type collection, Hawaiian Is.) (bars= 10 µm). Close views of isolated peltidia. 9. Mature peltidium with tips of mycobiont hyphae developed on the other side and emerging through the dichotomously branched Phycopeltis cells. 10. View of mature peltidia : one with the mycobiont layer easily seen within the « clenched fist » formed by the Phycopeltis cells (left) and lateral view of another one (right). 11-12. Views of both sides of immature peltidia : upper one with the « foot » of the dichotomously branched cells of Phycopeltis and lower one with the « clenched fist » formed by the same cells and « hemming in » the mycobiont cells.



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