[BGBM-Logo] Lichen determination keys
- Mycomicrothelia -
[BGBM-Foto klein]

Compiled key of Mycomicrothelia (40 species) / general remarks
by H. Sipman - 10 Sept. 2002, 3 May 2005


1a (If no special features, then go to 9) Foliicolous, with hypocuticular, lobed thallus (Perithecia in groups of 1-8, 0.1-0.2 mm wide and 0.1 mm tall; asci 40-50(-55) x 10-12(-15) mu; spores ca. 14 x 4 mu, smooth, dark brown; New Zealand) --- M. striguloides Sérus. & Aptroot
1b On bark or rarely wood --- 2

2a Ascospores muriform, except when juvenile or over-aged (Thallus pale brownish to whitish, with border lines; perithecia single, with wide fringe, 0.7-0.9 mm wide and ca. 0.2 mm tall; asci ca. 100 x 28 mu; spores 4 x 2-4 loculate, 25-35 x 12-15 mu, with rounded ends, smooth, grey; pycnidia absent; Cuba, New Guinea, Guyana, 100-500 m) --- M. decipiens (Müll. Arg.) R.C. Harris
2b Ascospores transversely septate --- 3

3a Hymenium inspersed with ca. 1-5 mu wide granules or droplets --- 4
3b
Hymenium clear --- 6

4a Spores under 28 mu long; pycnidia absent; lichexanthone absent (Thallus whitish grey, with border lines; perithecia single, with fringe, 0.3-0.5 mm wide and 0.1-0.3 mm tall, wall to 100 mu thick; hamathecium with oil droplets; asci 80-100 x 12-15(-25) mu; spores 24-28 x 8-10.5 mu, with almost equal locules, with rounded ends, verruculose; pycnidia absent; Trinidad, Costa Rica) --- M. oleosa Aptroot
4a Spores mostly over 30 mu long; pycnidia present; lichexanthone usually present --- 5

5a Perithecia ca. 0.5-0.7 mm wide (Thallus whitish to creamy, with border lines, sometimes with lichexanthone; perithecia single, with wide fringe, ca.0.5-0.7(-0.8) mm wide and 0.15-0.2 mm tall; hamathecium with oil droplets, these often restricted to less fertile parts; asci ca. 130-160 x 20-30 mu; spores ca. 30-40 x 10-14 mu, with slightly larger upper locule, with rounded ends, verruculose, olivaceous brown; pycnidia 75-125 mu wide, conidia bacilliform, simple, hyaline, ca. 12-15 x 0.8 mu; Venezuela, smooth bark of large branches.) --- M. xanthonica Komposch, Aptroot & Hafellner
5b Perithecia ca. 0.7-1.0 mm wide
(Thallus creamy white, with border lines, with lichexanthone; perithecia single, with wide fringe, ca. 0.7-1.1 mm wide and 0.3-0.4 mu tall; hamathecium with oil droplets, these mainly restricted to centre and margins; asci ca. 140-190 x 20-24 mu; spores ca. 30-45 x 10-15 mu, with slightly larger upper locule, with rounded ends, verruculose, olivaceous brown; pycnidia 75-125 mu wide, conidia bacilliform, simple, hyaline, ca. 15-21(-26) x 0.4 mu; Venezuela, smooth bark of large branches.) --- M. macrocarpa Komposch, Aptroot & Hafellner

6a Excipulum K+ crimson-red, dissolving (Thallus pinkish white, becoming whitish grey, with border lines; perithecia single, with fringe, ca. 0.5-0.7 wide and 0.1.0.2 mu tall; asci 45-80 x 11-14(-16) mu; spores 17-22 x (6-)7-10.5 mu, with upper locule about twice as large as lower locule, with rounded ends, minutely punctate-verruculose, olivaceous brown to red-brown; pycnidia mainly near the border lines, ca. 50 mu wide, conidia bacilliform, simple, hyaline, 2.5-3.5 x 1-1.5 mu; Mauritius, Costa Rica) --- M. leuckertii D. Hawksw. & J.C. David
6b Excipulum K+ olivaceous or K-, not dissolving or with yellow solution --- 7

7a Ostiole lateral; asci up to ca. 10 mu wide, with uniseriate spores (Thallus whitish, with border lines; perithecia single, usually oval, without fringe, 0.4-0.5 mm wide and ca. 0.15 mm tall, with lateral ostiole; asci ca. 130 x 10 mu; spores 18-22 x 6-7 mu, with equal locules or slightly larger upper locule, with rounded ends, verruculose, grey; pycnidia near the border lines, ca. 0.1 mm wide; conidia bacilliform, simple, hyaline, ca. 3 x 0.5 mu; Norfolk Island) --- M. lateralis INED.
7a Ostiole apical; asci over 10 mu wide, with (sub-)biseriate spores --- 8

8a Anthraquinone around ostiole (Thallus pinkish grey, without border lines; perithecia single, with fringe, 1.0-1.3 mm wide and 0.2-0.6 mu tall, young ostiole red, K+ (anthraquinone); wall completely carbonized, to 80 mu thick; asci ca. 150 x 20 mu; spores 23-29 x 11-14 mu, with equal locules, with rounded ends, verruculose; pycnidia 60-100 mu wide, conidia bacilliform, simple, hyaline?, 6-8 x 0.3-0.5 mu; Dominica) --- M. rubrostoma Aptroot
8b No anthraquinone present --- 9

9a (1) Ascospores small, most under 16 mu long --- 10
9b Ascospores medium-sized, most 16-22 mu long --- 22
9c Ascospores large, most 22-30 mu long --- 39
9d Ascospores very large, most over 31 mu long --- 44

10a Pycnidia present --- 11
10b Pycnidia absent --- 16

11a Thallus with border lines; pycnidia mainly near the border lines (Thallus brownish; perithecia in groups of 1(-3), with fringe, 0.4-0.7 mm wide and 0.1-0.3 mm tall; wall to 100 mu thick; asci 80-90 x 10-15 mu; spores (12-)15-18 x (6-)7-8 mu, with larger, rounded upper locule and often attenuated lower locule, smooth; pycnidia c. 0.1 mm wide, conidia not known; widespread in palaeotropics and neotropics, mostly at ca. 2000-3000 m.) --- M. punctata Aptroot
11b Thallus without border lines; pycnidia between the perithecia --- 12

12a Tropical taxon; thallus whitish (pale grey or pinkish); perithecia in groups of (1-)2-6 (Thallus whitish grey (-pale rose?), without border lines; perithecia with to 100 mu wide fringe, ca. 0.15-0.2 mm wide (groups to ca. 1 mm wide) and 0.08-0.12 mm tall, only ostiole exposed; involucrellum 10-15(-29) mu thick; asci 45-60 x 15-24 mu; spores 15-20 x 6-9 mu, with equal locules, with rounded or somewhat attenuated ends, delicately verruculose, brown; pycnidia between the perithecia, ca. 0.05 mm wide, conidia bacilliform, simple, hyaline, 12-15 x 0.5-1(-1.5) mu; Puerto Rico, Ecuador) --- M. socialis (Zahlbr.) D. Hawksw.
12b Temperate (European) taxa; thallus indistinct; perithecia mostly single --- 13

13a Perithecia (incl. fringe) ellipsoid, ca. 0.5-0.8 x 0.2-0.3 mm (Thallus indistinct; perithecia single, with ellipsoid, 300 mu wide fringe, 0.5-0.8 x 0.2-0.3 mm wide and 0.12-0.16 mm tall, only ostiole exposed; involucrellum 20-30 mu thick; asci 35-60 x 14-16(-20) mu; spores (12-)14-18(-20) x 6-8(-8.5) mu, little constricted, with equal locules, with rounded ends, slightly verruculose, dark brown; pycnidia between the perithecia or on separate thalli, 0.05-0.1 mm wide, conidia ellipsoid, polarilocular, hyaline, (9-)11-12.5(-14) x 4-6.5 mu; Europe, mostly on Betula.) --- M. wallrothii (Hepp) D. Hawksw.
13b Perithecia (incl. fringe) rounded --- 14

14a Pycnoconidia finally brown and 1-septate (Thallus indistinct; perithecia single, with fringe, 0.3-0.5mm wide and 0.1-0.125 mm tall, only ostiole exposed; involucrellum 5-15 mu thick; asci 42-50 x (15-)18-20(-26) mu; spores (12.5-)13.5-15.5(-17) x (6-)6.5-7.5(-8) mu, with equal locules, with rounded ends, verruculose, dark brown; pycnidia between the perithecia, 0.05-0.1 mm wide, conidia elongate-ellipsoid, finally 1-septate and brown, 13-14.5 x 5.5-6.5 mu; Central Europe, on Mespilus.) --- M. melanospora (Hepp) D. Hawksw.
14b Pycnoconidia persistently hyaline and simple --- 15

15a Pycnoconidia under 4.5 mm long (Thallus indistinct; perithecia single, with 30-50 mu wide fringe, (0.2-)0.3-0.4 mm wide and 0.09-0.12 mm tall; involucrellum 20-35 mu thick; asci 40-55 x 12-17 mu; spores (12.5-)13.5-16(-17.5) x (5.5-)6.5-8(-9) mu, with equal locules or slightly larger upper locule, with rounded ends, verruculose, olivaceous; pycnidia between the perithecia, 45-75 mu wide; conidia bacilliform, simple, hyaline, 3-4 x 0.5-0.7 mu; W Europe, on Corylus.) --- M. atlantica D. Hawksw. & Coppins
15b Pycnoconidia over 4.5 mm long
(Thallus indistinct; perithecia single, round to elliptic, with 50 mu wide fringe, ca. 0.3 mm wide and 0.06-0.08 mm tall, only ostiole exposed; involucrellum 9-12 mu thick; asci 45-62 x 12-16 mu; spores (11.5-)12.5-15(-17.5) x (4-)5-6(-7) mu, with equal locules or slightly larger upper locule, with rounded ends, verruculose, golden brown to brown; pycnidia between the perithecia, 30-50 mu wide, conidia bacilliform, simple, hyaline, 5-8 x 0.7-1.5 mu; Central Europe, on twigs and branches.) --- M. macularis (Hampe ex Massal.) Keissler

16a (10) Perithecia (incl. fringe) under 0.3 mm wide --- 17
16b Perithecia (incl. fringe) 0.3-0.5 mm wide --- 19
16c Perithecia (incl. fringe) over 0.5 mm wide
(Thallus pinkish grey, without border lines?; perithecia single, with fringe, 0.5-0.9 mm wide and 0.1-0.2 mm tall; wall to 150 mu thick; asci 60-80 x 10-15 mu; spores 14-17 x 4-6.5 mu, with larger upper locule, with rounded ends, verruculose; pycnidia absent; Indonesia 200 m.) --- M. alata Groenhart ex Aptroot

17a Perithecia without fringe (Thallus pale creamy brown, with border lines?; perithecia single, 0.2-0.25 mm wide and 0.08-0.11 mm tall; involucrellum 25-45 mu thick; asci 42-60 x 8.5-12 mu; spores 12.5-14(-15.5) x 4-5.5 mu, with equal locules or larger upper locule, with rounded ends, weakly constricted, weakly verruculose, pale olivaceous brown; pycnidia absent; Cuba, Australia, New Guinea.) --- M. exigua (Müll. Arg.) D. Hawksw.
17b Perithecia with distinct fringe --- 18

18a Thallus with distinct border lines; paraphyses ca. 2.5 mu thick (Thallus indistinct?; perithecia single, with purplish basal fringe, 0.2-0.3 mm wide and 0.07-0.11 mm tall; involucrellum 25-40 mu thick; asci 55-65 x 10-14 mu; spores (11-)12-14(-15) x (5-)5.5-6.5(-7.5) mu, with somewhat larger upper locule, with rounded to weakly attenuated ends, verruculose, pale brown to golden brown; pycnidia absent; China, Japan.) --- M. fumulosa (Zahlbr.) D. Hawksw.
18b Thallus without border lines; paraphyses 1-1.5 mu thick
(Thallus indistinct?; perithecia single, ca. 0.3 mm wide and 0.06-0.11 mm wide; involucrellum 14-35 mu thick; paraphyses 1-1.5 mu thick; asci 55-65 x 12-14 mu; spores (12.5-)13.5-15(-16) x (5.5-)6-6.5(-7) mu, with larger upper locule, with rounded ends, verruculose, olivaceous brown; pycnidia absent; China.) --- M. minutula (Zahlbr.) D. Hawksw.

19a Thallus without border lines, indistinct to whitish --- 20
19b Thallus with border lines, whitish to pinkish or pale brownish --- 21

20a Spores mostly below 15 mu long (Thallus indistinct?; perithecia single, ca. 0.3 mm wide and 0.06-0.11 mm tall; involucrellum 14-35 mu thick; paraphyses 1-1.5 mu thick; asci 55-65 x 12-14 mu; spores (12.5-)13.5-15(-16) x (5.5-)6-6.5(-7) mu, with larger upper locule, with rounded ends, verruculose, olivaceous brown; pycnidia absent; China.) --- M. minutula (Zahlbr.) D. Hawksw.
20b Spores mostly over 15.5 mu long
(Thallus whitish, without border lines; perithecia single, 0.3-0.4 mm wide and 0.12-0.15 mm tall; involucrellum 30-40 mu thick; asci 50-60 x 8-15 mu; spores (14-)15.5-17.5 x (6-)6.5-7.5 mu, with equal locules or slightly larger upper locule, with rounded ends, smooth to verruculose, olivaceous brown; pycnidia absent; India, Kerala.) --- M. nonensis (Stirt.) D. Hawksw.

21a Spores often under 15 mu long, with slightly unequal loculi; perithecia without fringe usually under 250 mu wide (Thallus whitish to pale rose, with border lines; perithecia single, with ca. 50 mu wide fringe, 0.4-0.5 mm wide and 0.06-0.1 mm tall; involucrellum 25-50 mu thick; asci 50-65 x 12-14 mu; spores 13.5-16 x 6-7 mu, with upper locule almost twice as large as lower locule, with rounded ends, verruculose, golden brown; pycnidia absent; pantropical.) --- M. subfallens (Müll. Arg.) D. Hawksw.
21b Spores rarely under 15 mu long, with strongly unequal loculi; perithecia without fringe usually over 250 mu wide
(Thallus whitish to pale brown, with border lines; perithecia single, with fringe, 0.4-0.5 mm wide and ca. 0.1-0.14 mm tall; involucrellum 35-45 mu thick; asci 65-80 x 12-15 mu; spores 14.5-17.5(-19) x 6-7.5 mu, with upper locule around twice as large as lower locule, with rounded ends, verruculose, brown; pycnidia absent; pantropical.) --- M. miculiformis (Nyl. ex Müll. Arg.) D. Hawksw.

22a (9) Pycnidia present --- 23
22b Pycnidia absent --- 27

23a Perithecia (incl. fringe) strongly ellipsoid, 0.5-0.8 x 0.2-0.3 mm; pycnoconidia ellipsoid, polarilocular (Thallus indistinct; perithecia single, with 300 mu wide, ellipsoid fringe, 0.5-0.8 x 0.2-0.3 mm wide and 0.12-0.16 mm tall, only ostiole exposed; involucrellum 20-30 mu thick.; asci 35-60 x 14-16(-20) mu; spores (12-)14-18(-20) x 6-8(-8.5) mu, weakly constricted, with equal locules, with rounded ends, scarcely verruculose, dark brown; pycnidia between the ascomata or on separate thalli, 50-100(-120) mu wide, conidia ellipsoid, polarilocular, hyaline, (9-)11-12.5(-14) x 4-6.5 mu; Europe, mostly on Betula.) --- M. wallrothii (Hepp) D. Hawksw.
23b Perithecia (incl. fringe) rounded; pycnoconidia bacilliform, simple --- 24

24a Perithecia mostly single, ca. 0.4-0.6 mm wide (incl. fringe) --- 25
24b Perithecia mostly in groups of (1-)2-6, under 0.3 mm wide (incl. fringe) --- 26

25a Perithecia 0.4-0.5 mm wide, with pore area exposed only; temperate USA (Thallus indistinct, with border lines; perithecia single or in groups of 2-3, with 50-100 mu wide fringe, 0.4-0.5 mm wide and 0.1-0.15 mm tall, only ostiole exposed; involucrellum 40-60 mu thick; asci 50-65 x 10-12 mu; spores 17-20(-21) x 7-8(-9) mu, with equal locules or with slightly larger upper locule, with rounded ends, verruculose, olivaceous brown; pycnidia between the perithecia and more dense near the border lines, 50-75 mu wide, conidia bacilliform, simple, hyaline, 3-4 x 1-1.5 mu; USA, Massachusetts.) --- M. willeyana (Müll. Arg.) D. Hawksw.
25b Perithecia 0.4-0.7 mm wide, completely exposed; tropical
(Thallus brownish, with border lines; perithecia single or in groups of 2-3, with fringe, 0.4-0.7 mm wide and 0.1-0.3 mm tall; wall to 100 mu thick; asci 80-90 x 10-15 mu; spores (12-)15-18 x (6-)7-8 mu, with larger, rounded upper locule, and often attenuated lower locule, smooth; pycnidia mainly near the border lines, c. 0.1 mm wide, conidia not known; widespread in palaeotropics and neotropics, mostly at ca. 2000-3000 m.) --- M. punctata Aptroot

26a Ascospores with equal locules (Thallus whitish grey (-pale rose?), without border lines; perithecia in groups of (1-)2-6, with to 100 mu wide fringe, ca. 0.15-0.2 mm wide (groups to ca. 1 mm wide) and 0.08-0.12 mm tall, only ostiole exposed; involucrellum 10-15(-29) mu thick; asci 45-60 x 15-24 mu; spores 15-20 x 6-9 mu, with equal locules, with rounded or somewhat attenuated ends, delicately verruculose, brown; pycnidia between the perithecia, 50-75 mu wide, conidia bacilliform, simple, hyaline, 12-15 x 0.5-1(-1.5) mu; Puerto Rico, Ecuador) --- M. socialis (Zahlbr.) D. Hawksw.
26b Ascospores with unequal locules
(Thallus brownish, border lines?; perithecia usually in groups of 2-3 confluent, sometimes with fringe, 0.2-0.35 mm wide and to 0.15 mm tall; involucrellum 20-30 mu thick; asci 65-75 x 12-14 mu; spores 17-22(-24) x 5.5-7.5 mu, with larger upper locule, with rounded ends, verruculose, pale olivaceous brown, without halo; pycnidia between the perithecia?, 75-100 mu wide, conidia bacilliform, simple, hyaline, 4-5 x 1-1.5 mu; New Zealand.) --- M. minutissima (Knight) D. Hawksw.

27a (22) Thallus border lines present --- 28
27b Thallus border lines absent --- 33

28a Asci over 80 mu long --- 29
28b Asci under 80 mu long --- 31

29a Ascospores under 20 mu long, sparsely punctulate (Thallus indistinct?, with border lines; perithecia single, with to 100 mu wide fringe, 0.5-0.6 mm wide and 0.12-0.25 mm tall; involucrellum 20-30 mu thick; asci 80-110 x 14-18 mu; spores 16-19.5 x 7.5-10(-10.5) mu, with upper locule more than twice as large as lower locule, with rounded ends, sparsely punctulated, dark olivaceous brown; pycnidia absent; California, Mimulus.) --- M. dothideaspora (Cooke & Harkn.) D. Hawksw.
29b Ascospores mainly over 20 mu long, (finally) verruculose --- 30

30a Asci under 22 mu wide (Thallus pale brown, with border lines; perithecia single, ca. 0.4 mm wide and 0.2-0.25 mm tall; involucrellum 30-50(-70 below) mu thick; asci 80-100 x 10-20 mu; spores 19-23(-27) x (7.5-)9-11(-12) mu, with larger upper locule, with rounded ends, verruculose, golden brown; pycnidia absent; India.) --- M. conothelena (Nyl.) D. Hawksw.
30b Asci over 22 mu wide
(Thallus creamy or whitish or indistinct, with border lines; perithecia single, with or without fringe, ca. 0.5 mm wide and 0.1-0.25 mm tall; involucrellum 30-70 mu thick; asci 80-90(-100) x (23-)26-31 mu; spores (17.5-)21-24(-26) x (7.5-)9-11.5(-13) mu, with larger upper locule, with rounded ends, verruculose, deep golden brown; pycnidia absent; neotropical, Philippines) --- M. thelena (Ach.) D. Hawksw.

31a (28) Ascocarps conical, over 150 mu high, without distinct fringe (Thallus whitish-rose, with border lines; perithecia single, 0.3-0.4 mm wide and 0.15-0.225 mm tall; involucrellum 50-65 mu thick; asci (55-)65-73 x (12-)13-14 mu; spores (13.5-)17-19(-21) x (5.5-)6.5-7.5(-8.5) mu, with equal locules or larger upper locule, with rounded (-attenuate) ends, verruculose. olivaceous brown; pycnidia absent; pantropical.) --- M. captiosa (Krempelh.) D. Hawksw.
31b Ascocarps flattened, under 150 mu high, with distinct fringe --- 32

32a Ascospores mostly under 17.5 mu long; tropical (Thallus whitish to pale brown, with border lines; perithecia single, with fringe, 0.4-0.5 mm wide and (0.08-)0.1-0.14 mm tall; involucrellum 35-45 mu thick; asci 65-80 x 12-15 mu; spores 14.5-17.5(-19) x 6-7.5 mu, with upper locule about twice as large as lower locule, with rounded ends, verruculose, brown; pycnidia absent; pantropical.) --- M. miculiformis (Nyl. ex Müll. Arg.) D. Hawksw.
32b Ascospores mostly over 17.5 mu long; oceanic Europe
(Thallus creamy or whitish, with border lines; perithecia single, 0.3-0.5 mm wide and 0.09-0.125 mm tall; involucrellum 25-40 mu thick; asci 55-70 x 12-18 mu; spores (15.5-)17.5-21(-25) x (6-)7-9(-10) mu, with equal locules or larger upper locule, with rounded or somewhat attenuated ends, verruculose, olivaceous brown; pycnidia absent; W. Europe.) --- M. confusa D. Hawksw.

33a (27) Perithecia (incl. fringe) over 0.5 mm wide --- 34
33b Perithecia (incl. fringe) under 0.5 mm wide --- 35

34a Perithecia rounded, with rounded fringe (Thallus pinkish grey, without border lines?; perithecia single, with fringe, 0.5-0.9 mm wide and 0.1-0.2 mm tall; wall to 150 mu thick; asci 60-80 x 10-15 mu; spores 14-17 x 4-6.5 mu, with slightly larger upper locule, with rounded ends, verruculose; pycnidia absent; Indonesia, 200 m) --- M. alata Groenhart ex Aptroot
34b Perithecia elliptic, with elliptic fringe
(Thallus indistinct; perithecia single, with elliptic, to 350 m wide fringe, ca. 0.6-1.0 x 0.3-0.4 mm wide and 0.15-0.2 mm tall; involucrellum 60-100 mu thick; asci (65-)70-100 x 15-20 mu; spores 18-22 x (7.5-)8.5-10.5 mu, with larger upper locule, with rounded ends, smooth, olive-brown to red-brown; pycnidia absent; France, California, Pakistan, on wood and twigs.) --- M. inaequalis (Fabre) D. Hawksw.

35a Perithecia (incl. fringe) under 0.3 mm wide; temperate zone of Europe (Thallus whitish, without border lines; perithecia single, ca. 0.2 mm wide and 0.1-0.12 mm tall, only ostiole exposed; invoucrellum 15-25 mu thick; asci 65-75 x 15-18 mu; spores (15-)16-18 x (6.5-)7-8(-9) mu, with equal locules or slightly larger upper locule, with broadly rounded ends, verruculose, dark brown; pycnidia absent; Europe, on Abies, Quercus.) --- M. pachnea (Körber) D. Hawksw.
35b Perithecia (incl. fringe) over 0.3 mm wide; tropical --- 36

36a Perithecium fringe 50-100 mu wide (Thallus indistinct; perithecia single, 0.4-0.5 mm wide and 0.1-0.17 mm tall, only ostiole exposed; involucrellum 30-50 mu thick; asci ?; spores (15.5-)17-19(-23) x 5-7 mu, with equal locules, with rounded ends, verruculose, olivaceous brown; pycnidia absent; neotropical, Hawaii.) --- M. anonacea (Müll. Arg.) D. Hawksw.
36b Perithecium fringe under 50 mu wide --- 37

37a Ascospores under 18 mu long (Thallus whitish, without border lines; perithecia single, 0.3-0.4 mm wide and 0.12-0.15 mm tall; involucrellum 30-40 mu thick; asci 50-60 x 8-15 mu; spores (14-)15.5-17.5 x (6-)6.5-7.5 mu, with equal locules or somewhat larger upper locule, with rounded ends, smooth to verruculose, olivaceous brown; pycnidia absent; India, Kerala) --- M. nonensis (Stirt.) D. Hawksw.
37b Ascospores mostly over 18 mu long --- 38

38a Perithecia flattened, not over 100 mu tall (Thallus olivaceous, without border lines; perithecia single, 0.2-0.4 mm wide and 0.07-0.09(-0.1) mm tall; involucrellum 20-35 mu thick; asci 63-67 x 17-20 mu; spores (17.5-)19-22(-23) x (8-)8.5-10(-10.5) mu, with equal locules or slightly larger upper locule, with rounded ends, verruculose, olive-brown; pycnidia absent; Mexico: Jalisco.) --- M. modesta (Müll. Arg.) D. Hawksw.
38b Perithecia conical
(Thallus indistinct; perithecia single, 0.2-0.4 mm wide, conical; asci ?; spores 21-22 x 8 mu, with rounded upper and attenuated lower end, verruculose; pycnidia absent; Brazil, on Fourcroya (Amaryllidac.).) --- M. pachytheca (Saccardo & Sydow) Aptroot

39a (9) Most ascospores under 9 mu wide --- 40
39b Most ascospores over 9 mu wide --- 41

40a Perithecia 0.8-1.0 mm wide, with 200-400 mu wide fringe (Thallus indistinct; perithecia in groups of 2-8 with common fringe, 0.8-1.0 mm wide and 0.12-0.17 mm tall; involucrellum 60-100 mu thick; asci ?; spores (21-)22-25 x 7.5-9(-10.5) mu, with equal locules or larger upper locule, with rounded ends, verruculose, golden brown; pycnidia absent; S. Africa, Fiji Islands) --- M. confluens (Müll. Arg.) D. Hawksw.
40b Perithecia 0.4-0.5 mm wide, without distinct fringe
(Thallus whitish, without border lines; perithecia single, 0.4-0.5 mm wide and 0.15-0.18 mm tall; involucrellum 35-60 mu thick; asci 75-90 x 12-18 mu; spores (21-)24-28(-30) x 5-9(-11) mu, with equal locules or slightly larger upper locule, with rounded ends, verruculose, sometimes with 2 pseudosepta, olivaceous brown; pycnidia absent; pantropical.) --- M. hemisphaerica (Müll. Arg.) D. Hawksw.

41a Asci under 20 mu wide --- 42
41b Asci over 20 mu wide --- 43

42a Most ascospores under 23 mu long, with rounded ends (Thallus pale brown, with border lines; perithecia single, ca. 0.4 mm wide and 0.2-0.25 mm tall; involucrellum 30-50(-70 below) mu thick; asci 80-100 x 10-20 mu; spores 19-23(-27) x (7.5-)9-11(-12) mu, with larger upper locule, verruculose, golden brown; pycnidia absent; India.) --- M. conothelena (Nyl.) D. Hawksw.
42b Most ascospores over 24 mu long, with attenuated ends
(Thallus whitish, without border lines; perithecia single, ca. 0.4 mm wide and 0.15-0.2 mm tall; involucrellum 40-80 mu thick; asci 90-120 x 14-16 mu; spores (22-)24-28(-29.5) x (8.5-)9-11.5(-12.5) mu, with larger upper locule, verruculose, reddish brown; pycnidia absent; Colombia) --- M. apposita (Nyl.) D. Hawksw.

43a Thallus with border lines (Thallus creamy or whitish or indistinct; perithecia single, with or without fringe, ca. 0.5 mm wide and 0.1-0.25 mm tall; involucrellum 30-70 mu thick; asci 80-90(-100) x (23-)26-31 mu; spores (17.5-)21-24(-26) x (7.5-)9-11.5(-13) mu, with larger upper locule, with rounded ends, verruculose, deep golden brown; pycnidia absent; neotropical and Philippines.) --- M. thelena (Ach.) D. Hawksw.
43b Thallus without border lines
(Thallus pinkish white, border lines?; perithecia single, 0.5-0.6 mm wide and 0.2-0.3 mm tall; involucrellum 45-60 mu thick; asci (65-)75-90 x 20-30 mu; spores (21-)22-28(-30) x (8.5-)9-11(-12) mu, with slightly larger upper locule, with rounded ends, often with 2 pseudosepta, verruculose, brown; pycnidia absent; palaeotropical and Dominica) --- M. obovata (Stirt.) D. Hawksw.

44a (9) Endospore layer thin and short-lived --- 45
44b Endospore layer thick and long-lasting
(Thallus whitish, with border lines; perithecia single, 0.8-1.1 mm wide and ca. 0.2-0.3 mm tall; asci 110-130 x 30 mu; spores 35-45 x 13-15 mu, with equal locules or slightly larger upper locule, with rounded ends, often with 2 pseudosepta, verruculose, grey; pycnidia between the perithecia and near the border lines; conidia not seen; Costa Rica, Colombia, New Guinea, Australia, on bark, 1300-1900 m) --- Ornatopyrenis queenslandica (Müll. Arg.) Aptroot

45a Hymenium partially inspersed --- 3a
45b Hymenium completely clear
(Thallus whitish?, without border lines; perithecia single, ca. 0.4 mm wide; asci 150-180 x 30-44 mu; spores 32-38 x 14-18 mu, with larger upper locule with rounded end and smaller lower locule with somewhat conical end, without pseudosepta, verruculose, grey; pycnidia and conidia not seen; Vienna (Austria)) --- Mycomicrothelia lojkae (Rehm) Y.Z. Wang, Aptroot & K.D. Hyde


General remarks / key

The key is compiled from information in the literature listed below. Additional information on M. punctata and M. leuckertii is based on material in herbarium B. Further information was provided by Dr. A. Aptroot, whose support is gratefully acknowledged.

This key is not part of an ongoing research project. It is just a tool for identification. Nevertheless I will be pleased to accept and incorporate suggestions for improvement, and will be even more pleased when somebody prepares a better version!

Knowledge of the genus is still very limited, in particular of the tropical representatives. Descriptions are often based on single or few specimens and for several species the characters and their range of variation are incompletely known. Therefore some of the taxa keyed out below may turn out to be synonyms.

Short characterisation of the genus:
- No supracortical thallus, this is completely endophloeiodic, sometimes forming whitish or pinkish patches, sometimes bordered by dark hypothallus lines, sometimes indistinct and not discolouring the bark surface.
- Perithecia usually single, simple, regularly scattered, occasionally coalescing in small groups; exciple carbonized, dimidiate, often with basal fringe, originating subepidermally, finally completely exposed, sometimes with only ostiole exposed, sometimes becoming sessile or even raised due to erosion of surrounding bark; carbonized parts in thin section dark (reddish) brown, K+ more or less strongly olivaceous; ostioles central in all but one species.
- Hamathecium gelatinous, I-negative, clear or in a few neotropical species inspersed with ca. 1-5 mu wide droplets or grains, with ca. 2 mm wide, sparsely septate, branched and anastomosing filaments, hardly branched at ascus level, said to be pseudoparaphyses; asci clavate to subcylindrical, I-negative, wall gradually thickening towards the tip, with small ocular chamber ca. 1/4 of ascus width.
- Spores 8/ascus or inconstantly in somewhat reduced number, olivaceous grey, becoming brownish at age, with one (sub)central euseptum, where they are constricted and a torus ring can sometimes be seen; internally an endospore layer can be seen against the spore wall in certain stages of the spore development; the endospore may protrude into the locule and form rings or transverse or occasionally longitudinal septa; outer surface covered with a more or less distinct gelatinous sheath (halo), at some stage verruculose or spinulose; lower cell usually smaller than upper cell.
- Pycnidia absent in some species, common in others, often concentrated along the hypothallus border lines. Most pycnidia are empty and pycnospores are not always known in species where pycnidia occur.

Related (non-lichenized) genera differ by one or more of the following characters: perithecium wall of cellular structure, K-; ascus with nipple in ocular chamber; hymenium I+ blue.

Mycomicrothelia species usually grow on smooth bark of young stems or branches in light, humid conditions. They tend to colonize large surfaces with a persistent mosaic of individuals.

Perithecium size is given in surface view, incl. clypeus/fringe (all carbonized parts); this deviates from Hawksworth (1985) values, which are without fringe.

 

Sources:

  • Aptroot, A. (1991): A Monograph of the Pyrenulaceae (Excluding Anthracothecium and Pyrenula) and the Requienellaceae, with Notes on the Pleomassariaceae, the Trypetheliaceae and Mycomicrothelia (Lichenized and Non-lichenized Ascomycetes). Bibliotheca Lichenologica 44. J. Cramer, Berlin, Stuttgart. 178 pages. (158 fig.)
  • Aptroot, A. (1995): Redisposition of some species excluded from Didymosphaeria (Ascomycotina). Nova Hedwigia 60 (3-4), 325-379.
  • David, J.C. & Hawksworth, D.L. (1995): Lichens of Mauritius I: some new species and records. pp. 93-111 in: Studies in Lichenology with Emphasis on Chemotaxonomy, Geography and Phytochemistry. Festschrift Christian Leuckert (Eds: Knoph, J.-G.; Schrüfer, K.; Sipman, H.J.M.). Bibliotheca Lichenologica 57. J. Cramer, Berlin, Stuttgart.
  • Harris, R.C. (1989): A sketch of the family Pyrenulaceae (Melanommatales) in eastern North America. Mem. New York Bot. Gard. 49, 74-107.
  • Hawksworth, D.L. (1985): A redisposition of the species referred to the ascomycete genus Microthelia. Bull. Brit. Mus. (Nat. Hist.), Bot. 14 (2), 43-181.
  • Komposch, H., Aptroot, A. & Hafellner, J. (2002): New species of lichenized and non-lichenized ascomycetes from a rainforest canopy in southern Venezuela. Lichenologist 34 (in press)
  • Müller Arg., J. (1885): Pyrenocarpeae Cubenses. Bot. Jahrb. Syst. 6, 375-421.
  • Sérusiaux, E. & Aptroot, A. (1998): Mycomicrothelia striguloides sp. nov. from New Zealand. The Bryologist 101 (1), 144-146.
  • Sipman, H.J.M. & Aptroot, A. (in prep.): Two new Mycomicrothelia species (Ascomycotina, Pleosporales).
  • Wang, Y.Z, Aptroot, A, & Hyde, K.D. 1994. Revision of the Ascomycete genus Amphisphaeria. Fungal Diversity Press.
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