The genus Echinostelium ( Myxomycetes ) in Lithuania

Seven species of the genus – Echinostelium apitectum, E. arboreum, E. brooksii, E. colliculosum, E. corynophorum, E. aff. elachiston, E. minutum – are reported from Lithuania. Their morphological peculiarities are discussed; a key to the species, pictures and distribution maps are given.


INTRODUCTION
The genus Echinostelium de Bary was erected in Ro s t a f i ń s k i (1873) for myxomycetes with very pale spores and stipitate minute sporocarps that rarely exceed 500 μm.Myxomycetes of the genus mostly inhabit bark of living trees and shrubs but can also be occasionaly found on litter including tiny branchlets or coniferous needles.Their sporocarps are especially fragile and usually short-living, therefore they are seldom collected in the field.Thus, for investigations of this group simple but highly efficient techniques of substrate incubation in the laboratory is very useful.So far 16 species have been described within the genus.One of them, E. vanderpoellii Nann.-Bremek., D. W. Mitch., T. N. Lakh.et R. K. Chopra, later was proposed to reduce to a synonym of E. apitectum K. D. Whitney (Pa n d o 1997).Another one, Echinostelium roseum Ing, was excluded because it appeared to be not a myxomycete (I n g 1984).In Lithuania the first records of Echinostelium species were obtained in late 1990'ies; up to now 7 species are known from the country: Echinostelium apitectum, E. arboreum, E. brooksii, E. colliculosum, E. corynophorum, E. aff. elachiston, E. minutum.All these species except for E. minutum are reported here for the first time for Lithuania.The paper also presents morphological, ecological and geographical data on Lithuanian Echinostelium species.

MATERIAL AND METHODS
Virtually all Echinostelium specimens described here were obtained from moist chamber cultures.W h i t n e y (1980) proposed a special protocol for revealing Echinostelium species; it includes substrate soaking for 1-3 hours, and further incubation in the dark at 12-15°C.In the present research the cultures were processed following H ä r k ö n e n (1977) because I aimed to reveal not only Echinostelium, but all myxomycetes which might inhabit a particular substrate.So, bark pieces cut from a living tree/shrub trunk or main branches were placed in one layer into Petri dishes lined with filter paper.The dishes were filled with distilled water and left closed for 24 hrs at room temperature in a natural light regime, then excess water was poured out.The dishes closed with covers were further kept in room temperature in a natural light regime and regularly checked for myxomycete sporocarps -on the first incubation week daily, later on once a week.Emerged sporocarps were allowed to dry slowly by slightly opening a lid and leaving for a night.Echinostelium species usually developed within first few days, but sometimes additional mass sporifications of E. minutum were observed after a considerable time.
Microscopic examination was carried out in fresh preparations in 3% KOH.Micrographs of sporocarps stained with Cotton Blue were made with a Pentax *istDS camera mounted on a Biolam-I microscope.Scanning electron micrographs were made from air-fresh material with Hitachi S2500 SEM at the Natural History Museum, London.Voucher specimens of the species are kept in the herbarium of the Institute of Botany, Vilnius (BILAS).
Bark pH was measured with IQ-150 pH-meter with ThermoRussel flat-head electrode KDCEF11 on the second day after water was removed.
Nomenclature of myxomycetes follows L a d o (2001).Standard forms of authors' names are according to B r u m m i t t and Po w e l l (1992).
NOTES.Echinostelium apitectum is rather variable species ranging from well-developed columella (bearing threads of capillitium) to strongly reduced or even absent columella.L a d o and Pa n d o (1997) distinguish two forms of E. apitectum: one with large (10-12 μm diam.) and the second with small (6-9 μm diam.)spores, sporocarps of the latter also being taller and more slender.But the authors admit that both forms merge, and for their taxonomical recognition further evidence would be needed.In the Lithuanian material of E. apitectum two groups can be distinguished, too.One group included stouter sporocarps with no apparent columella, spore-like body reaching 11-14 μm diam., and spores approx.6-7.5 μm diam., appearing warted under transmitted light (TL, oil immersion).The other one covered higher and more slender sporocarps with a smaller spore-like body (8-10 μm diam.), discernible columella, and slightly larger spores (7.5-8 μm diam.).But, similarly to L a d o and Pa n d o (1997) experience, there were also specimens transitional between both groups in the Lithuanian material, therefore all they were ascribed to E. apitectum.
In Lithuania E. apitectum was most frequently found on acid substrates: the highest number of collections was obtained from Pinus sylvestris bark which pH ranged from 3.7 to 4.6.The myxomycete was also found -albeit only sporadically -on bark of deciduous trees with higher pH (up to 6.3); one collection was found on bark with nearly neutral pH reaching 6.9.This experience rather supports results obtained by Wr i g l e y d e B a s a n t a ( 2004): in her model experiments of acid rain simulation E. apitectum sporulated on bark with lower pH values after treating it with solutions of pH 3 and 4.However, some authors report that E. apitectum was frequently collected from bark of Juniperus thurifera (L a d o 1993) and Olea europaea (Pa n d o 1989, l. c.Wr i g l e y d e B a s a n t a 2000) whose pH is significantly higher -5.5-6.5.
In both localities, bark for moist chamber cultures was collected in biologically rich forests.In Biržai district it was collected in the Botanical Reserve of Biržai For- Sporocarps gregarious, rosy when fresh, turning pale brown, 100-150 μm high; stalk hyaline in TL, partly filled with a refuse material; sporotheca 40-60 μm diam., spores loosely packed in the sporotheca; peridium evanescent, remaining as a small colar at the base of columella; columella hemispherical on a short stalk, brown, 4.5-6.5 μm diam.; spores rosy in mass, pale rosy in TL, appearing smooth, with a thinner germination area, 10.5-14 μm diam.
NOTES.Echinostelium brooksii is close to E. corynophorum; for differences columella and spores should be examined (see comments under E. corynophorum).
E. brooksii most frequently occurred on bark of Pinus sylvestris, together with Echinostelium apitectum and E. minutum.E. brooksii sporulated with the highest frequency on bark whose pH range was the same as for E. apitectum -from 3.7 to 4.6, but its general pH range was narrower: only a few collections were obtained from bark which pH was more than 5.0.So, this species appears to be confined to the most acid substrates among species of the g.Echinostelium.
SUBSTRATE.Bark of Fraxinus excelsior.pH 6.6-7.5.DISTRIBUTION.Akmenė distr., Vilnius city (Fig. 5).Rare, 4 records.NOTES.Echinostelium colliculosum is characterized by small sporocarps and thickened articular areas on the spore wall.From a very closely related species E. coelocephalum T. E. Brooks et H. W. Keller (which have not been registered in Lithuania, so far) it is said to differ in larger spores with less pronounced thickened areas, as well as in the colar form (W h i t n e y , K e l l e r 1980).Thus, in E. colliculosum collar is larger and its margins adhere to the spore-like body, while in E. coelocephalum collar margins appear to stay free.In specimens which are described here the colar was large, and its margins were attached closely to the spore-like body.But even under oil-immersion it was difficult to discern whether thickened areas on a spore-like body and spore walls were of the uniform thickeness (E.coelocephalum) or tapering towards edges (E.colliculosum).As the critical drying point technique was not applied while preparing material for SEM examination, these thickenings were not distinct in SEM photographs, too.
In Lithuania E. colliculosum was observed on bark of trees growing along roadsides; pH of the bark cultures was close to neutral.Bearing in mind that in western Kazakhstan steppe E. colliculosum was also collected from windbreak-forming trees with bark pH as high as 7.2-8.4(unpublished data), it appears that this species prefers substrata with neutral to slightly alkaline reaction.
SUBSTRATE.Alnus glutinosa female cones; pH 6.1.DISTRIBUTION.Tauragė distr.(Fig. 7).Rare, 1 record.NOTES.As noted by W h i t n e y (1980) Echinostelium corynophorum is closely related to E. brooksii.The author points at the following differences: columella in E. corynophorum is hyaline to pale yellow while in E. brooksii it is always deeply dark; spores of E. corynophorum bear thickenings and are white, meanwhile spores of E. brooksii are smooth and rosy.For distinguishing these two species L a d o and Pa n d o (1997) suggest one more particular trait: the thinnest part of E. corynophorum stalk is in a short distance below the collar, and the thinnest section of E. brooksii stalk is right below the colar.In the only specimen from Lithuania which is described here the thinnest area of the stalk was not well distinguished, the size of sporotheca and columella were on the smaller end of the scale for the species, but spores bore distinct thickened areas.The shape of columellae of E. brooksii and E. corynophorum collected in Lithuania differed markedly: the first was hemispherical, or horizontally lenticular, and the second was subglobose.
SUBSTRATE.Bark of Fraxinus excelsior.DISTRIBUTION.Biržai distr.(Fig. 5).Rare, 2 records.NOTES.Echinostelium elachiston is characterized by small, yellow tinted sporocarps, a wide collar on the tip of stalk, scanty to absent capillitium, and spores of 6.5-8 μm diam.M a r t i n and A l e x o p o u l o s (1969) state that spores of this species are smooth with well-marked thickened circular areas on the wall, while W h i t n e y (1980) specifies that they are minutely roughened and lacking circular thickenings.Spores of specimens from Spain described by L a d o and Pa n d o (1997) also are said to have smooth wall of uniform thickness, but their measurements reach up to 11 μm diam.Warts on spore wall of both available Lithuanian specimens were very conspicuous, particularly when stained with Cotton Blue, and spores were in general larger than it is noted in the species protologue.All other characteristics of these specimens rather well agreed with the concept of E. elachiston.
Substrate pH was not measured for available specimens of E. aff.elachiston, but data show that pH of bark of Fraxinus excelsior growing in natural conditions is close to 5.5-6 (unpublished data).
NOTES.Small sporocarps of Echinostelium minutum with scanty capillitium can resemble E. apitectum, however the latter species has a spore-like body.
E. minutum is the most common species of the genus recorded in almost all regions of Lithuania where myxomycetes were investigated.Its sporocarps readily appeared in moist chamber cultures on a great variety of substrata with a wide range of pH from highly acidic to nearly neutral.But most frequently its sporification was observed at pH 3.4-6.1.If the cultures were kept for sufficiently long time, additional waves of E. minutum sporification occured.E. g, in a culture of moose dung sporocarps of this species were noted 3 months after setting the culture, then the next sporification occurred three and a half months after the first sporification.One more sporification took place 10 months after setting the culture, but sporocarps were scanty.This phenomenon was not observed for other Echinostelium species, although it was noted for Physarum viride (Bull.)Pers.var.aurantium (Bull.)Lister, Arcyria cinerea (Bull.)Pers.