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Department of Applied Biology, P.O. Box 27, FIN-00014 University of Helsinki, Finland
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ABSTRACT |
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The new species Chaenothecopsis nigripunctata (Mycocaliciaceae, Ascomycota) is described from western North America. The fungus grows on resin and wetwood of Tsuga heterophylla in moist temperate forests. It differs from its relatives in the regular production of polycephalic ascomata with contiguous capitula. The species is further characterized by a well-developed mazaedium. An unevenly thickened epithecium acts to compartmentalize the mazaedium into several columns per apothecial disk. Dark spore masses against the pale epithecium give the fungus a highly distinctive, elegant appearance. This species is not easily accommodated in Chaenothecopsis in a traditional sense but it is placed in this genus pending a better understanding of relationships within the Mycocaliciaceae.
Key words: exudate, resinicolous fungi, Tsuga heterophylla, westen hemlock, wetwood
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIAL AND METHODSTAXONOMYDISCUSSIONLITERATURE CITED |
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, Tibell 1984). Most resinicolous species grow on conifers; they have been collected from species of Abies Mill., Larix Mill., Picea A. Dietr., Pinus L., Sequoia Endl., Sequoiadendron Buchholz, and Tsuga Carrière (Bonar 1971, Tibell and Titov 1995, Rikkinen 1999, Selva and Tibell 1999, Titov 1998, 2001). Some resinicolous species are widely distributed, but most of them appear to be restricted to East Asia or western North America. The group has a long evolutionary history, as exemplified by a fossilized specimen in European amber dating back to 20–40 million years ago (Rikkinen and Poinar 2000). |
MATERIAL AND METHODS |
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Stand level data on the distribution of the new fungus were collected on June 5, 1998, in the T. T. Munger Research Natural Area at the Wind River Experimental Forest in the southern Washington Cascades. The site has a mean annual precipitation of 2528 mm and a mean annual temperature of 8.7 C (Lyons 1998). The study site is an old-growth forest of Pseudotsuga menziesii (Mirb.) Franco-T. heterophylla with emergent Douglas fir dominating the upper canopy and western hemlocks filling in the middle and lower canopies; tree ages in the stand are estimated to range up to 460 yr old. The old Douglas firs are gradually being replaced by western hemlocks and other shade-tolerant tree species in gap-phase succession. The basal trunks (0–2.5 m) of all trees on five 25 m x 25 m sample plots were checked for the presence of resinicolous fungi. Two sample plots represented a moist T. heterophylla/Athyrium filix-femina (L.) Roth community type (subplots 011, 013), while the others represented drier T. heterophylla/Gaultheria shallon Pursh (subplots 206, 316) and T. heterophylla/Berberis nervosa Pursh-G. shallon (subplot 109) community types. A total of 83 tree trunks of equal or greater than 5 cm diam. (DBH) were studied, 78 of which were western hemlocks. Data on tree heights were available from the Wind River Canopy Crane Research Facility.
The specimens were identified according to methods of classical herbarium taxonomy, including examination under dissecting and compound microscopes. Micrographs were obtained using a Jeol JSEM-830 scanning electron microscope in the Institute of Biotechnology, Electron Microscopy Unit, University of Helsinki. Ascospore, ascus, and hyphal measurements were made from squash mounts of ascomata in water. Ascomata height, capitulum diameter, and stalk width were measured from dry ascomata under incident light. Specimens used for all measurements were chosen arbitrarily but without preconceived basis.
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TAXONOMY |
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HOLOTYPE. Rikkinen 98428 (H), ISOTYPES Rikkinen 98428 (UPS), Rikkinen 98428 (US).
On exudate of conifers (Tsuga heterophylla). Ascomata variable in size, usually 0.8–2.0 mm high. Capitulum lenticular to subhemispheric, (0.25)0.45–0.80(0.90) mm diam. (n = 30), usually polycephalic, formed of 2–8 (12) congregated disks; individual disks (0.25)0.30–0.55(0.58) mm diam. (n = 30). Epithecium with a highly reflective surface, partly thickened by groups of perpendicularly arranged, densely agglutinated hyphae. Excipulum well developed, 10–30 µm thick, confluent between neighboring disks in compound capitula, consisting of periclinally arranged, somewhat swollen hyphae. Hymenium hyaline, clearly delimited from dark stalk hyphae. Mazaedium well developed, dark brown, spores kept together by a thin mucilage. Mature spores extruded between epithecial thickenings, forming multiple mazaedial columns; later the mazaedial elements enlarge and coalesce. Stalks smooth, usually straight, rather stout, (0.07)0.09–0.17(0.20) mm in diam. (n = 30), uppermost part pale, basal section blackish. Outermost layer of stalk formed by pale, irregularly arranged, senescent hyphae, and often covered by a thin pruina of hyphal remains. Inner part of stalk dark, formed by slightly interwoven, largely periclinally arranged hyphae. All parts of the apothecium KOH-. Asci cylindrical, 80–110 x 5–7 µm, with a strongly thickened apex penetrated by a canal. Ascospores uniseriate, obliquely oriented in semi-mature asci and more periclinally oriented in mature asci, 1-septate, brown, ellipsoidal, smooth (11.5)13.0–15.5(17) x (4.5)5–5.5(6) µm (length: x = 14.31, n = 50; width: x = 5.24, n = 50).
Specimens examined. USA. OREGON: Linn County, Horse Rock Ridge Research Natural Area, dense old-growth forest with T. heterophylla, P. menziesii, and Thuja plicata Donn on steep N-facing slope, 44°18'N, 122°52'W, elev 740 m, on exudate of T. heterophylla, 25 May 1998, Rikkinen 98482 (HOLOTYPE, H), Rikkinen 98482 (ISOTYPE, UPS), Rikkinen 98482 (ISOTYPE, US), Rikkinen 98481 (PARATYPE, OSC). Linn County, Hackleman Grove, old-growth P. menziesii–T. heterophylla–Abies amabilis (Dougl.) Forbes forest, 44°23.89'N, 122°05.60'W, elev 1100 m, on exudate of T. heterophylla, 23 June 1998, Rikkinen 98658, 98659, 98664 (H). WASHINGTON: Skamania County, Thorton T. Munger Research Natural Area, Whistle Punk Trail, moist T. heterophylla dominated forest bordering seasonally flooded Fraxinus latifolia Benth. swamp, 45°49'N, 121°58'W, elev ca 350 m, on exudate of T. heterophylla, 5 June 1998, Rikkinen 98496, 98500 (H). Skamania County, Wind River Canopy Crane Research Facility, dense old-growth forest with T. heterophylla (lower and middle canopy) and P. menziesii (upper canopy), Th. plicata, and A. amabilis, 45°49.14'N, 121°57.07'W, elev 355 m, on exudate of T. heterophylla, 5 June 1998, Rikkinen 981328, 981338, 982217, 982227, 982237, 983473, 983485, 98298W, 98342W (H).
Chaenothecopsis nigripunctata has only been found growing on the exudate and wetwood of T. heterophylla in forests of the Pacific Northwest. It thrives in humid microhabitats and commonly occurs in deep shade. It prefers damaged or suppressed trees in old-growth forests.
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DISCUSSION |
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This type of development has not been described from other members of the Mycocaliciaceae. However, many species of Chaenothecopsis and Mycocalicium Vain. can produce irregular or lobulate capitula, especially in old ascomata. The development of lobulate capitula is caused by some irregularity in the long-continued production of asci. Asci tend to first mature in specific sections of the hymenium. As more and more asci mature, the hymenium expands and the capitulum surface tends to become convex. Spatial and temporal irregularities in ascus production may in turn lead to the development of several hymenial convexities per capitulum. However, such convexities are usually contiguous and not delimited by bundles of thickened hyphae as in C. nigripunctata.
Chaenothecopsis nigripunctata also differs from most of its relatives in the regular production of polycephalic ascomata. Branching occurs at the stalk tip, with each short branch forming a separate apothecial head. Profuse branching leads to the development of compound capitula, consisting of several, partially contiguous apothecial heads. Branched ascomata are rather common in the Mycocaliciaceae, especially in resinicolous species with long stalks. Species like Chaenothecopsis sitchensis Rikkinen and C. dolichocephala Titov can even form multi-layered groups via branching and proliferation through old hymenia (Tibell and Titov 1995, Rikkinen 1999). Also, some undescribed species from western North-America and East Asia commonly produce branched stalks. However, most of these taxa have relatively narrow and long stalks, tend to branch at various levels, and rarely, if ever, produce compound capitula akin to those of C. nigripunctata. While some Chaenothecopsis species with stout stalks can occasionally branch near the tip, Mycocalicium sequoiae Bonar seems to be the only other species known to produce clusters of apothecial heads on a common stalk. Even this species tends to branch lower and thus have longer branches and less confluent apothecial heads than C. nigripunctata. Mycocalicium sequoiae is further characterized by large apothecia originating from a common pseudostroma, small and non-septate spores, and by a yellowish-green pruina of vulpinic acid on the capitulum surface (Bonar 1971, Tibell and Titov 1995).
As in many other mazaedial fungi, C. nigripunctata is probably mainly dispersed by invertebrates and other animals (Rikkinen 1995, Rikkinen and Poinar 2000). The smooth ascospores are held together by an amorphous substance. The apothecial disks of C. nigripunctata also have a unique, strongly refractive surface layer and the multiple dark spore masses against this pale surface make the species instantly recognizable. In spore and ascus size, C. nigripunctata resembles some Phaeocalicium species more than it does Chaenothecopsis as traditionally conceived (Tibell 1996). The 1-septate ascospores are ellipsoidal, quite large and dark brown. The narrowly cylindrical asci are very long and formed singly from ascogenous hyphae. Young asci have a strongly thickened apex penetrated by a long, narrow canal. In mature asci the apical thickenings are less conspicuous and the canals are shorter and more blunt. Thus, while C. nigripunctata does not perfectly fit into Chaenothecopsis in a traditional sense, its inclusion in this genus is proposed pending further study of generic relationships in the Mycocaliciaceae.
Ecology and distribution –
Chaenothecopsis nigripunctata has only been found growing on trunks of wounded T. heterophylla. It has been collected from the resin and wetwood of large wounds, such as beaver scars, as well as from small wounds, like those associated with branch stubs. The visible characteristics of wetwood have been evident in all hemlocks bearing the ascomata of C. nigripunctata. Wetwood is characterized by a darker color and wetter appearance than normal heartwood, and it has a distinctive, somewhat fragrant odor. Hemlock wetwood is known to be higher in specific gravity (owing to lignin extractives that coat the pit membranes and lumen walls of wood cells), extractive chemicals, and moisture content than surrounding normal heartwood (Schroeder and Kozlik 1972, Hillis 1987, Shaw et al 1995, Hennon and DeMars 1997). The increased extractive content of the wetwood is appreciable, amounting to a five-fold increase over that of adjacent normal heartwood, and this increase is general for all classes of extractives found in T. heterophylla. Another characteristic of wetwood is the presence of microorganisms. Some of these are able to produce a range of aliphatic acids and various gases (Schroeder and Kozlik 1972, Hillis 1987). The causes and processes leading to formation of wetwood are not perfectly understood, but wetwood is known to be consistently associated with trees that have wood decay. Wetwood is thought to block the vertical movement of pathogenic fungi by plugging the tracheids. The wet condition aids in blocking vertical movement of aerobic fungi by creating anaerobic or near anaerobic conditions. Additionally, the bacteria and other microbes that are present in wetwood may produce compounds that antagonize decay fungi. Thus, while bacteria and some fungi are commonly present in Tsuga wetwood, decay fungi are usually not. Species of Tsuga are easily susceptible to the formation of wetwood. Other conifers in which wetwood is commonly observed include species of Abies, but the condition may also develop in several other genera (Schroeder and Kozlik 1972, Hillis 1987, Shaw et al 1995, Hennon and DeMars 1997).
While little is known regarding the nutritional requirements of the resinicolous Mycocaliciaceae or factors limiting their growth, it is evident that C. nigripunctata is consistently associated with wetwood of Tsuga. In this habitat, it occurs frequently with Pycnostysanus resinae (Fr.) Lindau and other dematiaceous hyphomycetes. Interestingly, C. nigripunctata has not yet been found growing together with other resinicolous species of Chaenothecopsis that are also found on western hemlock in the Pacific Northwest (C. asperopoda Titov, C. edbergii Selva and Tibell, and C. tsugae Rikkinen) (Rikkinen 1999, Selva and Tibell 1999).
While Chaenothecopsis nigripunctata has only been collected from four sites in Oregon and Washington, it may be a rather widely distributed, overlooked species. Western hemlock is a common and widely distributed conifer in the Pacific Northwest. Most specimens of C. nigripunctata have been collected from the T. heterophylla Zone (Franklin and Dyrness 1988). Structurally similar forests extend from British Columbia to northern California and mantle the Coast Range and lower western slopes of the Cascade Range. Chaenothecopsis nigripunctata has also been found from a montane forest on the western slope of the Cascade Range (Abies amabilis Zone). Similar forests extend from British Columbia to the central Oregon Cascades and isolated stands are also found on high peaks of the northern Oregon Coast Ranges.
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ACKNOWLEDGMENTS |
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FOOTNOTES |
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Accepted for publication May 5, 2002.
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LITERATURE CITED |
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TOPABSTRACTINTRODUCTIONMATERIAL AND METHODSTAXONOMYDISCUSSIONLITERATURE CITED |
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Franklin JF, Dyrness CT., 1988 Natural vegetation of Oregon and Washington. Oregon, USA: Oregon State University Press. 452 p
Hennon PE, DeMars DJ., 1997 Development of wood decay in wounded western hemlock and Sitka spruce in southeast Alaska. Can J For Res 27:1971-1978
Hillis WE., 1987 Heartwood and tree exudates. Giessen, Germany: Springer-Verlag. 240 p
Lyons B., 1998 Crown structure and spatial distribution of epiphytes on western hemlock, Wind River, WA [MS Dissertation]. The Evergreen State College, Washington. 104 p
Rikkinen J., 1995 What's behind the pretty colours? A study on the photobiology of lichens. Bryobrothera 4:1-239
———. 1999 Two new species of resinicolous Chaenothecopsis (Mycocaliciaceae) from western North America. Bryologist 102:366-369
———, Poinar G., 2000 A new species of resinicolous Chaenothecopsis (Mycocaliciaceae, Ascomycota) from 20 million year old Bitterfeld amber, with remarks on the biology of resinicolous fungi. Mycol Res 104:7-15
Schmidt A., 1970 Anatomisch-taxonomische Untersuchungen an europäishen Arten der Flechtenfamilie Caliciaceae. Mitteilungen der Staatinstitut Allgemein Botanik Hamburg 13:111-166
Schroeder HA, Kozlik CJ., 1972 The characterization of wetwood in western hemlock. Wood Science and Technology 6:85-94
Selva SB, Tibell L., 1999 Lichenized and non-lichenized calicioid fungi from North America. Bryologist 102:377-397
Shaw DC, Edmonds RL, Littke WR, Browning JE, Russel KW., 1995 Incidence of wetwood and decay in precommercially thinned western hemlock stands. Can J For Res 25:1269-1277
Tibell L., 1984 A reappraisal of the taxonomy of Caliciales. Nova Hedwigia Beih 79:597-713
———. 1996 Phaeocalicium (Mycocaliciaceae, Ascomycetes) in northern Europe. Ann Bot Fennici 33:205-221
———, Titov A., 1995 Species of Chaenothecopsis and Mycocalicium (Caliciales) on exudate. Bryologist 98:550-560
Titov A., 1998 New and rare calicioid lichens and fungi from relict tertiary forests of Caucasus and the Crimea. Folia Cryptogamia Estonica 32:127-133
———. 2001 Further notes on calicioid lichens and fungi from the Gongga Mountains (Sichuan, China). Lichenologist 33:303-314
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