Microsoft Word - Islam and Irfanullah13_2_.doc Bangladesh J. Plant Taxon. 13(2): 111-129, 2006 (December) HYDROBIOLOGICAL STUDIES WITHIN THE TEA GARDENS AT SRIMANGAL, BANGLADESH. VI. DESMIDS (XANTHIDIUM, ARTHRODESMUS, STAURODESMUS AND STAURASTRUM) A.K.M. NURUL ISLAM AND HASEEB MD. IRFANULLAH1 Department of Botany, University of Dhaka, Dhaka-1000, Bangladesh Key words: Acidic habitats, Species diversity, Conservation, Phytoplankton, New records Abstract In this last instalment of the series, 78 desmid taxa belonging to four genera, namely Xanthidium (8 taxa), Arthrodesmus (3 taxa), Staurodesmus (11 taxa) and Staurastrum (56 taxa) have been recorded from different aquatic habitats located within the tea gardens at Srimangal, Maulvi Bazar. Of these, nine are described as new records for Bangladesh. An overall assessment of the algal flora of the study area reveals desmids as the single largest group consisting of 230 taxa out of 421 recorded algal taxa. The paper comments on the conservation potentials of the studied aquatic habitats as monitoring tools of land use pattern like tea-gardening. Introduction In a series of hydrobiological papers, Islam and Irfanullah have recently described the aquatic macrophytes (Islam and Irfanullah 2000) and the major proportion of the algal flora (Islam and Irfanullah 2005a, b, c, 2006) of some selected habitats within the tea gardens at Srimangal, Maulvi Bazar District. The present paper is the concluding instalment of this series dealing with four desmid genera, namely, Xanthidium, Arthrodesmus, Staurodesmus and Staurastrum, from these aquatic habitats. Materials and Methods The studied water bodies (described in Islam and Irfanullah 2000), namely, Baraoora Lake, the Burburia River, ditches and paddy fields were mainly acidic (Islam and Irfanullah 2005a). A total of 120 algal samples were collected in different seasons of 1996 and 1997: winter (9 January 1996 and 6 January 1997), spring (18 March 1997), rainy season (20 July 1997) and autumn (20 October 1997). The methods of sample collection, preservation and subsequent examination were described by Islam and Irfanullah (2005a). Taxonomic enumeration This study revealed 78 desmid taxa belonging to four genera, of which nine are new records for Bangladesh. The new records are marked with asterisks. Eighteen desmid taxa belonging to the mentioned four genera have already been reported from this area by the 1Corresponding author. Present address: The World Conservation Union (IUCN), Bangladesh Country Office, House 11, Road 138, Gulshan 1, Dhaka-1212, Bangladesh. E-mail: hmirfanullah@yahoo.co.uk 112 ISLAM AND IRFANULLAH same authors as new records for Bangladesh (Islam and Irfanullah 1998, 1999), thus are not marked in this account. Remaining other taxa are briefly described along with their spatial and temporal occurrence, and abundance. Class: Chlorophyceae; Order: Zygnematales; Family: Desmidiaceae Genus: Xanthidium Ehrenberg 1. X. acanthophorum Nordst. (Pl. 1, Fig. 4) (Islam 1970, 928, 14: 4) L. csp. 59.4 µm, L. ssp. 44.5 µm, W. csp. 46 µm, W. ssp. 37.8 µm, I. 12 µm. Lake (autumn 1997) and river (spring 1997); rare. 2. X. burkillii W. & W. fa. (Pl. 1, Fig. 5) L. csp. 74.2-78.3 µm, L. ssp. 52.6-54 µm, W. csp. 87.7; W. ssp. 59.4-61.4 µm. I. 23 µm. Differs from Islam and Haroon (1980, 582, 16: 232) in the ornamentations at front view. Lake; winter 1996; few. 3. X. hastiferum Turner var. javanicum (Nordst.) Turner (Islam and Irfanullah 1999, 103, 3: 31) Lake; autumn 1997; rare. 4. X. hastiferum var. javanicum fa. planum Turner (Islam and Irfanullah 1999, 103, 3: 30) Lake; autumn 1997; few. 5. X. spinosum (Josh.) W. & W. fa. (Pl. 1, Fig. 2) L. ssp. 50 µm, W. ssp. 48.6 µm, W. csp. 54 µm, I. 25.6 µm. Ten pairs of spine not regularly arranged as described by Islam and Haroon (1980, 584, 16: 226-227). Lake (winter 1996 and spring 1997; few) and river (winter 1997; rare). 6. X. spinosum (Josh.) W. & W. var. (Pl. 1, Fig. 3) L. 47.2 µm, W. ssp. 44.5 µm, W. csp. 48.6 µm, I. 24.3 µm. Small spines are irregularly, sparsely distributed all over the cell surface. River; spring 1997; rare. 7. X. urniforme (W. & W.) Scott & Croasdale (Pl. 1, Fig. 1) (Islam and Haroon 1980, 586, 13: 177) L. csp. 44.5 µm, L. ssp. 41.8 µm, W. csp. 41.8-44.5 µm, W. ssp. 39 µm, t. csp. 25.6 µm, t. ssp. 23 µm, I. 17.5 µm. Paddy field and river; autumn 1997; few to rare. 8. Xanthidium sp. (Pl. 1, Fig. 6) L. csp. 61 µm, L. ssp. 47 µm, depth 23.5-24.7 µm. River; spring 1997; rare. HYDROBIOLOGICAL STUDIES WITHIN THE TEA GARDENS 113 Plate 1 (Figs. 1-6) 1. Xanthidium urniforme, 2. X. spinosum fa., 3. X. spinosum var., 4. X. acanthophorum, 5. X. burkillii fa., 6. Xanthidium sp. [Scales = 20 µm] Genus: Arthrodesmus Ehrenberg 9. A. asperies Scott & Croasdale fa. (Islam and Irfanullah 1999, 95, 2: 17-18) Lake; winter 1996; few. 10. *A. curvatus Turner var. latus Scott & Prescott (Pl. 2, Fig. 8) (Scott and Prescott 1961, 76, 33: 1-3) L. 36.4 µm, W. csp. 70.2-73 µm, W. ssp. 39-41.8 µm, I. 13.5 µm. Lake; winter 1996; common. 114 ISLAM AND IRFANULLAH 11. A. curvatus Turner fa. (Pl. 2, Fig. 7) L. 36.4 µm, W. csp. 64.8-66 µm, W. ssp. 35-37.8 µm, I. 8 µm. Our form differs from Hirano (1972, 142, 7: 3) in narrow isthmus and angular sides. Side’s angles are comparable with Corasdale and Scott’s Staurodesmus indentatus (W. & W.) Teil. (1976, 542, 12: 1). Lake; winter 1996; few. Genus: Staurodesmus Teiling 12. Std. dejectus (Bréb.) Teil. var. dejectus fa. (Islam and Irfanullah 1999, 96, 4: 45-46) Lake; winter 1996; rare. 13. Std. dickiei (Ralfs) Lillier var. circularis (Turner) Croasdale (Islam and Irfanullah 1999, 96, 4: 39-40) Lake; autumn 1997; common. 14. Std. dickiei var. circularis fa. (Islam and Irfanullah 1999, 97, 4: 41-42) Lake; winter 1996 and 1997; rare to common. 15. Std. dickiei var. maximus (W. West) Thom. (Islam and Irfanullah 1999, 97, 4: 37-38) Lake; winter 1996; common. 16. Std. hebridarus (W. & W.) Förster var. hebridarus (Islam and Irfanullah 1999, 98, 4: 43-44) Lake; winter 1997; few. 17. Std. megacanthus (Lund.) Thunk. (Pl. 2; Fig. 12) (Ling and Tyler 1986, 53, 26: 5-7) L. 46 µm, W. csp. 58.8-68.2 µm, W. ssp. 44.7-50.5 µm, I. 11.8 µm. Lake; winter 1996; few. 18. Std. pachyrhynchus (Nordst.) Teiling (Islam and Irfanullah 1998, 94, 2: 16) Lake; winter 1997; few. 19. Std. unicornis (Turner) Thomasson var. ceylanicum W. & W. fa. (Islam and Irfanullah 1999, 98, 3: 32-33) Lake; autumn 1997; few. 20. Std. unicornis (Turner) Thomass. var. gracilis (Iyenger & Vimala Bai) Teil. (Croasdale and Scott 1976, 543, 14: 3) (Pl. 2, Fig. 10) L. 30.3 µm, W. csp. 34.3-36.4 µm, W. ssp. 25.6-28.3 µm, I. 7.4 µm. Lake; winter 1996; few. HYDROBIOLOGICAL STUDIES WITHIN THE TEA GARDENS 115 Plate 2 (Figs. 7-15) 7. Arthrodesmus curvatus fa., 8. A. curvatus var. latus, 9 & 11. Staurastrum leptodermum var. ikapoae, 10. Staurodesmus unicornis var. gracilis, 12. Std. megacanthus, 13. Staurastrum sp., 14. St. leptacanthum var. brachyurum, 15. St. freemanii fa. [Scales = 20 µm] 116 ISLAM AND IRFANULLAH 21. Staurodesmus sp. (Pl. 3, Fig. 26) L. 27.5 µm, W. 22.5-25 µm, I. 11.7 µm. Granules are concentrically arranged on each arm as well as on the poles. Shape is similar to Std. pachyrhynchus (Nordst.) Teiling (Islam and Irfanullah 1998, 94, 2: 16). Lake; winter 1997; very rare. 22. Staurodesmus sp. (Pl. 7, Fig. 70) L. 27.5 µm, W. csp. 25.8-27.5 µm, I. 7.5 µm. Lake; winter 1997; rare. Genus: Staurastrum Meyen 23. St. alternans Bréb. (Islam and Irfanullah 1999, 94, 2: 11-13) Lake; autumn 1997; rare. 24. St. alternans Bréb. fa. (Pl. 4, Fig. 37) L. 27 µm, W. 25 µm, I. 8.5 µm. River; spring 1997; rare. 25. St. bifidum (Ehr.) Bréb. (Pl. 7, Figs. 59 & 60) (Ling and Tyler 1986, 38, 28: 17 & 18) L. 43.2 µm, W. csp. 63.4-68.8 µm, W. ssp. 40.5-43.2 µm, I. 14-16 µm, cell wall punctuate, divergent processes on each arm tip. Ours are larger than Ling and Tyler’s specimens. Lake; winter 1996; common. 26. St. bifidum (Ehr.) Bréb. fa. (Pl. 3, Fig. 28) L. 32.4-37.8 µm, W. csp. 32.4-46 µm, W. ssp. 28.3-32 µm, I. 13.5-14.8 µm; smooth wall, flat poles. The distance between the level of spines and the level of isthmus is twice as much the distance between the level of spines and the level of the pole of a semicell. Lake (winter 1997, common) and river (spring 1997, few). 27. St. brevispinum Bréb. fa. (Pl. 7, Fig. 68) L. 25 µm, W. csp. 29-30 µm, W. ssp. 26.7-28 µm, I. 5.8 µm. Semi-cells broader and length-wise compressed compare with Hirano’s (1959a, 289, 38: 7) material. Lake; winter 1996; rare. 28. St. ? cerastes Lund. (Pl. 6, Fig. 48) (Hirano 1959b, 371, 50: 1) L. 37.8 µm, W. cpr. 50.5 µm, I. 7.4 µm, t. 9.4 µm. Lake; autumn 1997; rare. 29. St. ceylanicum W. & W. Paddy field; autumn 1997; few. 30. St. coarctatum Bréb. var. subcurtum Nordst. (Pl. 3, Fig. 27) (Islam and Irfanullah 1999, 96, 2: 15 & 16) Lake; winter 1996; few. HYDROBIOLOGICAL STUDIES WITHIN THE TEA GARDENS 117 Plate 3 (Figs. 16-30) 16-18. Staurastrum orbiculare var. depressum, 19. St. retusum var. boreale, 20. St. disputatum var. sinense fa., 21 & 22. Staurastrum sp., 23. St. disputatum var. sinense, 24. St. disputatum var. extensum, 25. St. punctulatum, 26. Staurodesmus sp., 27. Staurastrum coarctatum var. subcurtum (after Islam and Irfanullah, 1999), 28. St. bifidum fa., 29. St. ensiferum, 30. Staurastrum sp. [Scales = 10 µm] 118 ISLAM AND IRFANULLAH 31. *St. ? crenulatum (Näg.) Delp. (Pl. 6, Fig. 53) (Scott and Prescott 1961, 88, 59: 10) L. 25 µm, W. csp. 37.5 µm, W. ssp. 30.8 µm, I. 8 µm. Lake; winter 1997; few. 32. *St. ? cyclacanthum W. & W. (Pl. 6, Fig. 54) W. csp. 48.6-52.6 µm, W. ssp. 40.5-43.2 µm, I. 8 µm. Top view is similar to St. cyclacanthum var. armigerum of Scott and Prescott (1961, 89, 57: 1-3). Lake; winter 1996; rare. 33. St. disputatum W. & W. var. extensum (Borge) W. & W. (Pl. 3, Fig. 24) (Islam and Haroon 1980, 588, 17: 238 & 239) L. 24.3 µm, W. 27.7 µm, I. 8 µm. River; spring 1997; few. 34. St. disputatum W. & W. var. sinense (Lütkm.) W. & W. (Pl. 3, Fig. 23) (Skuja 1949, 157, 36: 1 & 2) L. cpr. 27 µm, W. cpr. 27-28.3 µm. I. 10.8 µm. Lake (winter 1996) and river (spring 1997); few. 35. St. disputatum var. sinense fa. (Pl. 3, Fig. 20) L. 20.2 µm, W. 17.5 µm, I. 5.4 µm. Comparable with Hirano (1959b, 298, 39: 3). Paddy field; autumn 1997; rare. 36. St. ensiferum Turner (Pl. 3, Fig. 29) (Turner 1892, 109, 14: 22; Ling and Tyler 1986, 40, 39: 23-26) L. ssp. 48.6 µm, W. csp. 46-48 µm, W. ssp. 35 µm, I. 9.4 µm. River; spring 1997; few. 37. St. forficulatum Lund. (Pl. 4, Fig. 34) (Islam and Haroon 1980, 588, 21: 328 & 329) L. csp. 27 µm, L. ssp. 23 µm, W. csp. 23 µm, W. ssp. 20.2 µm, I. 12 µm. Paddy field; autumn 1997; common. 38. St. freemanii W. & W. (Islam and Irfanullah 1998, 94, 2: 17) Lake; autumn 1997; rare. 39. St. freemanii W. & W. fa. (Pl. 2, Fig. 15) L. 28.3 µm, W. cpr. 70.2 µm, W. spr. 37.8 µm, I. 9.4 µm, t. spr. 17.5 µm, t. cpr. 36.4 µm. Granulated cell wall; two additional spines alternately located on each semicell. Paddy field; autumn 1997; rare. 40. St. gemelliparum Nordst. (Pl. 4, Fig. 35) (Islam and Haroon 1980, 588, 20: 324 & 325) L. csp. 25.6 µm, L. ssp. 20.2 µm, W. csp. 24.3 µm, W. ssp. 16.2 µm, I. 8 µm. Young cell (?). Lake; winter 1997; rare. HYDROBIOLOGICAL STUDIES WITHIN THE TEA GARDENS 119 Plate 4 (Figs. 31-38) 31. Staurastrum tohopekaligense, 32 & 36. St. quadrangulare var. contectum, 33. St. leptacanthum var., 34. St. forficulatum, 35. St. gemelliparum, 37. St. alternans fa., 38. St. pseudosebaldi var. planctonicum. [Scales = 20 µm] 120 ISLAM AND IRFANULLAH 41. *St. glabrum (Ehr.) Ralfs var. glabrum (Pl. 7, Fig. 69) (Scott et al. 1965, 53, 11: 154) L. 25-29.7 µm, W. cpr. 39-46 µm, W. spr. 29.7-37.8 µm, I. 6-6.7 µm. Also comparable with Turner’s (1892, 17: 12) St. curvirostrum Turner. Lake; winter 1996; few. 42. St. gladiosum Turner (Pl. 7, Fig. 63) (Ling and Tyler 1986, 41, 32: 24 & 25) L. csp. 37.8 µm, L. ssp. 30.3 µm, W. csp. 41 µm, W. ssp. 27 µm, I. 8.8 µm. Paddy field; autumn 1997; rare. 43. St. javanicum (Nordst.) Turner var. apiculiferum (Turner) Krieger (Islam and Irfanullah 1998, 94, 2: 18-20) Lake; winter 1996; very rare. 44. St. laceratum Turner fa. (Pl. 6, Fig. 56) W. csp. 54-58.7 µm, I. 14.8 µm. Differs from Islam and Haroon (1980, 590, 8: 125 & 126) in arms having 3 terminal spines and 3-4 dorsal spines instead of 2 on both cases. Lake; winter 1996; rare. 45. St. leptacanthum Nordst. var. leptacanthum (Islam and Irfanullah 1999, 96, 2: 14) Paddy field; autumn 1997; rare. 46. St. leptacanthum Nordst. var. brachyurum Scott and Grönbl. (Pl. 2, Fig. 14) (Islam and Haroon 1980, 590, 21: 347 & 348) W. spr. 31 µm, W. cpr. 45.9 µm. Six arms in the upper ring and nine arms in the lower ring. River; spring 1997; rare. 47. St. leptacanthum Nordst. var. (Pl. 4, Fig. 33) L. cpr. 59.4 µm, L. spr. 50 µm, W. cpr. 48.6 µm, W. spr. 27 µm, I. 14.8 µm. Bears larger number of arms: the lower ring has 12 and the upper one has 8 arms. River; spring 1997; few. 48. St. leptocladum Nordst. var. cornutum Wille (Pl. 6, Fig. 47) (Islam and Haroon 1980, 590, 17: 243) L. 37.8 µm, W. cpr. 85 µm, W. spr. 12 µm, I. 9.4 µm. Lake; winter 1996; common. 49. St. leptodermum Lund. var. ikapoae (Schmidle) W. & W. (Pl. 2, Figs. 9 & 11) (Grönblad et al. 1958, 41, 20: 73 ; Hirano 1972, 149, 6: 8) Broad form (Fig. 9): L. csp. 54-56.7 µm, L. ssp. 40.5-41.8 µm, W. ssp. 33.7-35 µm, I. 13.5 µm, t. csp. 24.3-21.6 µm. Lake; winter 1996; few. Elongated form (Fig. 11): L. csp. 50 µm, L. ssp. 45 µm, L. pole-pole 31 µm, W. 32.4 µm, I. 13.5 µm. Lake; winter 1997; rare. However, Förster (1964, 33: 14-15) named the elongated form St. ikapoae Schm. var. elongatum (Grönblad & Scott) Förster. HYDROBIOLOGICAL STUDIES WITHIN THE TEA GARDENS 121 Plate 5 (Figs. 39-46) 39 & 40. Staurastrum sexangulare var. asperum, 41 & 42. St. sexangulare fa., 43. St. sexangulare ? var. bidentatum, 44. St. ? pinnatum, 45. St. sexangulare var. subglabrum, 46. St. pinnatum ? var. subpinnatum. [Scale = 20 µm] 122 ISLAM AND IRFANULLAH 50. St. longibrachiatum (Borge) Gutw. (Pl. 6, Fig. 50) (Ling and Tyler 1986, 42, 31: 24-26) L. 36.4 µm, W. csp. 64.8-74.2 µm, W. ssp. 60.7-70.2 µm, I. 9.4 µm. Lake; winter 1996 and autumn 1997; few. 51. *St. ? mucronatus (Ralfs) Croasdale (Pl. 7, Fig. 62) (Förster 1969, 71, 30: 16) L. 27 µm, W. csp. 35 µm, W. ssp. 25.6-27 µm; each arm is terminated with a small spine directed outward parallel to the flat cell pole. Lake; winter 1997; few. 52. St. orbiculare (Ehr.) Ralfs var. depressum Roy & Biss. (Pl. 3, Figs. 16-18) (Scott and Prescott 1961, 100, 52: 12; Scott et al. 1965, 56, 12: 170; Islam and Haroon 1980, 590, 8: 129 & 130, 17: 253 & 254) L. 27-38.5 µm, W. 24.3-37.8 µm, I. 6.7-10.8 µm. Pitted cell wall. Lake (winter 1996 and autumn 1997; few to common) and river (spring 1997; few). 53. St. orbiculare var. ralfsii W. & W. (Islam and Irfanullah 1998, 95, 2: 14) Lake; winter 1996; rare. 54. *St. ? peristephes Scott and Prescott (Pl. 6, Fig. 55) L. 47.2 µm, W. cpr. 56.7 µm, I. 12 µm. The top view is similar to Scott and Prescott’s material (1961, 100, 59: 5), but the front view of our specimen was not sufficient to confirm other details. Lake; autumn 1997; common. 55. *St. perundulatum Grönbl. (Pl. 7, Fig. 65) (Scott and Prescott 1961, 101, 52: 9; Förster 1969, 90, 36: 7 & 8) L. 11.5 µm, W. cpr. 34.4 µm, W. spr. 10 µm, I. 6 µm. Lake; autumn 1997; rare. 56. St. pinnatum Turner ? var. subpinnatum (Sch.) W. & W. (Islam and Haroon 1980, 590, 20: 320 & 321) (Pl. 5, Fig. 46, Pl. 7, Fig. 66) W. 51.6–57.4 µm, I. 14 µm. Lake; winter 1996 (few) and autumn 1997 (rare). 57. St. ? pinnatum Turner (Pl. 5, Fig. 44) (Islam and Haroon 1980, 590, 19: 290 & 291) W. cpr. 48.2 µm, W. spr. 18.5 µm, I. 13.5-14 µm. Lake; autumn 1997; rare. 58. *St. pseudosebaldi Wille var. planctonicum Teil. (Pl. 4, Fig. 38) (Förster 1974, 181, 28: 4) L. 30.4 µm, W. cpr. 46-52.6 µm, W. spr. 12.2-14.8 µm, I. 8 µm, t. 12.8 µm. Lake; autumn 1997; rare. HYDROBIOLOGICAL STUDIES WITHIN THE TEA GARDENS 123 Plate 6 (Figs. 47-56) 47. St. leptocladum var. cornutum, 48. St. ? cerastes, 49. Staurastrum sp., 50. St. longibrachiatum, 51. St. subsuecicum, 52. St. sonthalianum, 53. St.? crenulatum, 54. St. ? cyclacanthum, 55. St. ? peristephes, 56. St. laceratum fa. [Scales = 20 µm] 124 ISLAM AND IRFANULLAH 59. St. punctulatum Bréb. in Ralfs (Pl. 3, Fig. 25) (Scott and Prescott 1961, 104, 52: 14) L. 27-28.3 µm, W. 31 µm, I. 9.4 µm. River; spring 1997; few. 60. St. quadrangulare Bréb. var. contectum (Turner) Grönbl. (Pl. 4, Figs. 32 & 36) (Islam and Haroon 1980, 592, 21: 330 & 331) L. csp. 33.7 µm, L. ssp. 27 µm, W. csp. 33-40.5 µm, W. ssp. 23 µm, I. 10-11.5 µm. Lake; winter 1996; few. 61. St. retusum Turner var. boreale W. & W. (Pl. 3, Fig. 19) (Ling and Tyler 1986, 44, 29: 21 & 22) L. 17.5 µm, W. 16.7 µm, I. 5.8. Lake; winter 1996; common. 62. St. sexangulare Lund. var. asperum Playf. (Pl. 5, Figs. 39 & 40) (Scott and Prescott 1961, 107, 45: 1-3; Islam 1970, 931, 17: 18) L. cpr. 89 µm, L. spr. 56.7 µm, W. cpr. 94.5 µm, W. spr. 43.2 µm, I. 19 µm, t. cpr. 81 µm, t. spr. 35 µm. River; spring 1997; few. 63. St. sexangulare Lund. ? var. bidentatum Gutw. (Pl. 5, Fig. 43) (Scott and Prescott 1961, 107, 45: 4 & 5) L. spr. 31 µm, W. cpr. 47.2 µm, I. 9.4 µm. Smaller than typical. Lake; autumn 1997; rare. 64. St. sexangulare Lund. ? var. subglabrum W. & W. (Pl. 5, Fig. 45) (Scott and Prescott 1961, 107, 46: 1 & 2) W. csp. 75.6-81 µm. Lake; winter 1996; rare. 65. St. sexangulare Lund. fa. (Pl. 5, Figs. 41 & 42) L. spr. 35.8 µm, W. cpr. 52.6-60 µm, I. 11.5 µm. Smaller cell with 5 pairs of processes. Close to St. sexangulare var. subglabrum W. & W. (Scott and Prescott 1961, 107, 46: 1 & 2; Ling and Tyler 1986, 46, 34: 13 & 14). Lake; autumn 1997; rare. 66. St. sonthalianum Turner (Pl. 6, Fig. 52) (Turner 1892, 14: 27) L. 40.5 µm, W. cpr. 70.2-73 µm, I. 10.2 µm. Lake; winter 1996; rare. 67. St. subgracillimum W. & W. ? var. tortum Scott and Grönbl. (Pl. 7, Fig. 61) (Ling and Tyler 1986, 46, 32: 10-12) W. csp. 37-43.5 µm. I. 4.5 µm. Lake; autumn 1997; rare. 68. *St. subsuecicum Scott & Prescott (Pl. 6, Fig. 51) (Scott and Prescott 1961, 110, 52: 3) L. 33.7, W. cpr. 51.3-54 µm, I. 8 µm. Paddy field; autumn 1997; few. HYDROBIOLOGICAL STUDIES WITHIN THE TEA GARDENS 125 Plate 7 (Figs. 57-70) 57 & 58. Staurastrum wildemanii, 59 & 60. St. bifidum, 61. St. subgracillimum ? var. tortum, 62. St. ? mucronatus, 63. St. gladiosum, 64. Staurastrum sp., 65. St. perundulatum, 66. St. pinnatum ? var. subpinnatum, 67. Staurastrum sp., 68. St. brevispinum fa., 69. St. glabrum var. glabrum, 70. Staurodesmus sp. [Scales = 20 µm] 126 ISLAM AND IRFANULLAH 69. St. tohopekaligense Wolle (Pl. 4, Fig. 31) (Islam and Haroon 1980, 592, 17: 236 & 237) L. cpr. 70.2 µm, L. spr. 40.5 µm, W. cpr. 67.5-77 µm, W. spr. 31-32.4 µm, I. 17.5 µm. Lake; winter 1996; common. 70. St. tohopekaligense fa. minus (Turner) Scott & Prescott (Islam and Irfanullah 1999, 96, 3: 35 & 36) Lake; winter 1996; few. 71. St. wildemanii Gutw. (Pl. 7, Figs. 57 & 58) (Ling and Tyler 1986, 48, 28: 5 & 6, 11 & 12) L. 54 µm, W. csp. 85 µm, W. ssp. 54 µm, I. 20.2 µm. Spines are shorter than Ling and Tyler’s (1986) two-spined forms. Lake; winter 1996; few. 72. St. zahlbruckneri Luetk. (Islam and Irfanullah 1998, 95, 2: 15) Lake; winter 1997; rare. 73. Staurastrum sp. (Pl. 2, Fig. 13) W. 22.7 µm, I. 6.25 µm. Lake; winter 1997; rare. 74. Staurastrum sp. (Pl. 3, Figs. 21 & 22) L. 18.3-19.2 µm, W. 18.3-19.2 µm, I. 5.4-5.8 µm. Four or five droopy processes, punctuate cell wall. Processes of St. paulense var. ornatum Krieger as shown by Förster (1964, 425, 29: 8) are not long enough like our material, but show droopiness. Lake; autumn 1997; common. 75. Staurastrum sp. (Pl. 3, Fig. 30) L. 35 µm, W. 28.3-31 µm, I. 8 µm. Lake; autumn 1997; few. 76. Staurastrum sp. (Pl. 6, Fig. 49) L. 18.3 µm, W. 26.7 µm, I. 5 µm. Lake; autumn 1997; rare. 77. Staurastrum sp. (Pl. 7, Fig. 64) W. cpr. 39.5 µm. Top view similar to St. manfeldtii Delp. (Hirano 1959b, 368, 48: 1). Lake; winter 1996; few. 78. Staurastrum sp. (Pl. 7, Fig. 67) W. cpr. 64.8–67.5 µm, I. 12 µm. Lake; winter 1996; rare. The study area as a whole was extraordinary in terms of algal species richness (Table 1). Desmid diversity was remarkable, as expected in acidic waters, species number occupying more than half of the total species number. Most of the algal taxa (>50%) were HYDROBIOLOGICAL STUDIES WITHIN THE TEA GARDENS 127 microplankton (size 20-200 µm) followed by nannoplankton (size <20 µm) and epiphytes (around 40 taxa each). Habitat-wise, Baraoora Lake had more taxa (mean number about 75) than the Burburia River (mean number around 30). The lake showed highest number of species in winter (>140 taxa), whereas the river showed maximum in spring (>75 taxa). The lowest species number (around 40 taxa) in spring was quite unusual for a lentic water-body like Baraoora Lake. The river was highly dynamic in rainy season explaining the lowest species richness in monsoon (<10 taxa). Table 1. Relative abundance of different algal classes recorded from the aquatic habitats within the tea gardens at Srimangal, based on Islam and Irfanullah (2005 a, b, c, 2006 and the present paper). Algal Classes No. of genera No. of species No. of taxa Relative abundance by taxa (%) Cyanophyceae 17 28 28 6.7 Euglenophyceae 5 33 37 8.8 Chloromonadophyceae 1 1 1 0.2 Chlorophyceae (excluding desmids) 42 76 83 19.7 Chlorophyceae (desmids only) 25 182 230 54.6 Charophyceae 2 3 3 0.7 Xanthophyceae 8 11 11 2.6 Chrysophyceae 4 4 4 1.0 Bacillariophyceae 17 20 20 4.8 Dinophyceae 2 2 2 0.5 Rhodophyceae 1 2 2 0.5 Total 124 362 421 100 Discussion Conservation of algal communities lies with their habitat conservation. But it is difficult to peruse the stakeholders for conservation without direct and immediate benefits, which is often monetary. In many cases it is hard to prove the direct benefits of ‘a species’. In case of microscopic organisms, like algae, it is even tougher. If we argue that saving a species is essential for maintaining ecological integrity, many species will lose their importance as they might not be crucial in maintaining the functioning of their native ecosystems (Lawton 1991). But we believe that habitats like Baraoora Lake are important just because of the species diversity they possess. It is just like a living laboratory for aquatic biologists. Deepening this habitat and trying something financially profitable, like aquaculture, should not be encouraged (Of course, given the acidic pH, fish-culture might not be practical, anyway). Instead we should leave these habitats in their present state without any major interventions. Because of high species diversity, these can be used as ‘natural tools’ for monitoring the ecological quality of the tea gardens as a whole. Islam and Irfanullah (2005a) also emphasised on more systematic sampling and quantitative 128 ISLAM AND IRFANULLAH estimation of species abundance to get a clearer and detailed picture of the algal flora of these interesting habitats. Institute like the Bangladesh Tea Research Institute (BTRI) can take initiatives to run simple analyses of water chemistry and plankton community on a regular basis and share the information with the tea garden owners. This will assist the latter to assess the ecological impacts of current tea cultivation practices (e.g. nutrient-holding capacity of the soil, major changes in the soil chemistry, effects of chemical residues, etc.). Correlating the tea garden soil chemistry with lake water chemistry and biology will also help them to trace the viability of tea garden ecosystems. Baraoora Lake could be one of the first sites for the ecological monitoring of catchment-lake connectivity in Bangladesh. A full limnological investigation in these habitats will strengthen the justification of these habitats becoming monitoring tools. Acknowledgements The authors are grateful to Mr. A.F.M. Badrul Alam, the then Director, Bangladesh Tea Research Institute (BTRI), Srimangal, Maulvibazar for providing the logistic, laboratory and other support during this study and also to all his colleagues who extended their help in the laboratory and in supplying necessary information. Thanks are also due to James Finley & Co. for the permission to sample its aquatic habitats. Prof. Moniruzzaman Khondker, Department of Botany, University of Dhaka helped in reconfirming the new records. References Croasdale, H. and Scott, A.M. 1976. New or otherwise interesting desmids from Northern Australia. Nova Hedwigia 27(3-4): 501-596. Förster, K. 1964. Desmidiaceen aus Brasilien. 2 Teil: Bahia, Goyaz, Piauhy und Nord-Brasilien. Hydrobiologia 23(3-4): 321-505. Förster, K. 1969. 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