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This paper deals with a taxonomic study of two diatoms collected in Xizang (Tibet)
and, based upon the peculiarities of their rapheal system, a new taxonomic system of the Class Pennatae is proposed.
One of the diatoms was found in fifteen specimens collected in various localities (alt. 4100--5300 m) in eight counties in southern, western and northern Xizang, and has been identified as Amphiraphia xizangensis Chen et Zhu, a new genus and a new species, including a variety, major Chen et Zhu. This species is epiphytic in habit (sometimes becomes freefloating) and characterized by its two valves of a frustule dissimilar in structure: the epitheca has a dotted-line shaped shaphe with a more or less reduced central nodule and without the polar nodules, whereas the hypotheca has a typical raphe with both the well developed central nodule and polar nodules. These most striking structures have not been discovered in all the known species. Thus, based upon the pecularities of this genus, the authors have established not only a new family, Amphiraphiaceae Chen et Zhu, but also a new order, Amphiraphidales Chen et Zhu.
The other is a well known and widely distributed species, Rhoicosphenia curvata (Kütz.) Grun. This genus has always been placed in the Achnanthaceae. As We know that the alga does not have frustules with a pseudoraphe on one valve and a true raphe on the other as stated by Boyer (1927) and Smith (1950). In fact, it has only a rudimentary short raphe near each pole on the epitheca and a fully developed raphe on the hypotheca as mentioned by Cleve-Euler (1958), Hustedt (1962), and Patrick and Reimer (1966) and obse rved by the authors in the Xizang specimens. The alga is really similar to Amphiraphia xizangensis Chen et Zhu in having two valves dissimilar in rapheal type. Thus, based upon its generic characteristics the authors have established another new family, Rhoicospheniaceae Chen et Zhu, and placed it in the order Amphiraphidales Chen et Zhu too.
Regarding the systematic position of the Amphiraphidales, the following principles are considered:
1. It is evident that the free-floating or motile diatoms existing in the geological periods are really older than the epiphytic ones. This has been proved by some discoveries of the fossil diatoms.
2. Both epitheca and hypotheca of frustule of all the free-living diatoms, induding both centric and pennate species, are symmetrical in both valves and girdle-views, but, the epiphytic forms are usually asymmetrical, especially in a girdle-view.
3. The characteristics of rapheal system are often used by former algologists as a main taxonomic basis for considering category of pennate diatoms and affinity among them. The authors agree with this consideration.
4. In this paper Hustedt's classification of pennate diatoms is used as a basis for considering the phylogenetic problems of these diatoms, but the authors cite Schütt's Class Pennatae, instead of Hustedt's order Pennales; Sieminska's orders, Araphidales, Raphidioidales, Monoraphidales, and Biraphidales, instead of Hustedt's Suborders, Araphidineae, Raphidioidineae, Monoraphidineae, and Biraphidineae.
5. The rapheal system on the epitheca of the Amphiraphidales is really a reduced
structure derived from a typical form represented by the Biraphidales, and may be regarded as a transitional type from that of the Biraphidales to that of Monoraphidales.
6. Owing to the epitheca of the type genus Rhoicosphenia Grun. of the family Rhoi-
cospheniaceae lacking the central nodule and a great part of its axial area becoming a pseudoraphe, the authors consider that the family is more close to Monoraphidales than Amphiraphiaceae is in phylogeny.
According to the principles set forth above, a taxonomic system of the Pennatae is proposed as follows:
Class Pennatae Schütt
Order I. Araphidales Siem.
Order II. Raphidioidales Siem.
Order III. Biraphidales Siem.
Order IV. Amphiraphidales Chen et Zhu, ord.nov.
Family I. Amphiraphiaceae Chen et Zhu, fam. nov.
Family 2. Rhoicospheniaceae Chen et Zhu, fam. nov.
Order V. Monoraphidales Siem. 相似文献
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本文概述了植物分类学家胡先骕在发现植物新种水杉中的贡献;他在上世纪五十年代批判李森科,倡导摩尔根遗传学说的动因,及其科学、人文背景;最后,作为新文化运动中《学衡》派主力和唯一的科学家,本文对他的新人文主义思想做一简介和评述。 相似文献
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李承森 《中国科学院研究生院学报》1982,20(3):331-342
A new psilophytic plant, Hsüa robusta, is found in the Xujiachong Formation
(Emsian) of the Lower Devonian from the Qüjing (= Kütsing) district of Yunnan,
China. This plant is tentatively referred to the Cooksoniaceae of Rhyniales.
Hsüa gen. nov.
Type species: Hsüa robusta (Li et Cai) C. S. Li.
Diagnosis: Plants erect and then creeping. Main axes dividing pseudomonopodial-
ly and bearing dichotomous lateral branches which somewhat differentiate into vegeta,
tire and fertile ones, with dichotomous root-like and rhizophore-like appendages. Spo-
rangia terminal, round to reniform or wide reniform, dehiscing along distal margin into
two equal halves. Spores homosporous, trilete. Stomata anomocytic. Protostele cen-
trarch.
Hsüia robusta (Li et Cai) C. S. Li, comb. nov.
Cooksonia zhanyiensis Li et Cai, Acta Geologica Sinica, 52 (1) 1978, p. 10, pl. II,
fig. 6.——Taeniocrada robusta Li et Cai,ib. p. 10, pl. II, fig. 7—14.
Diagnosis: Characters same as in generic diagnosis. Main axes 6—10 mm wide and
at least 24 cm long, with vascular strands 1.2—2.4 mm acr oss. Fertile branches 3—4
times equally or unequally dichotomous, 10—1.5 mm in width and up to 11 cm in length,
possessing a vascular bundle of 0.5 mm in its greatest diameter. Branches circinately
coiled in apical regions. Axial tubercles, root-like and rhizophore— like appendages aris-
ing from the main axes usually anterior to the lateral branches. Axial tubercle round
with a diameter of 2.2—2.4 mm, having a vascular bundle about l mm across. Root-
like branches 3 times bifurcate, 1—0.3 mm wide and up to 1.5 cm long, with a vascular
bundle about 0.1 mm across. Rhizophore-like appendages forked, 3—1.7 mm in width,
possessing a vascular bundle of 0.7 mm in its greatest diameter. Root-like protuberances
sometimes arising from rhilzophore-like branches. Epidermal cells of axes generally
elongate, measuring 60—290μby 25—60 μ. Stomata mainly fusiform, 90—110 μ long
and 50—60μ wide, consisting of a pair of guard cells enclosing a pore 6—15μ in length
and 1—3μ in width. Cuticle of guard cells quite thick. Stomatal density about 5 per
mm2. Sporangia 0.8—4.2 mm high, 1.0—8.2 mm across, usually having a dehiscent distal
border which measures 50—100μ broad. Demarcation between sporangium and its stalk
quite clear. Epidermal cells of basal part of sporangial walls elongate, about 100 μ long
and 30μ wide, but those of distal part isodiametrally polygonal, about 50μ in diame-
ter. Stomata, radially arranged scattering over sporangial walls, generally round about
50μ in diameter and 50 per sporangium. Spores round, 18—36μ (average 27μ) indiameter, and smooth. Tracheids of protoxylem about 10μ across; those of metaxylem
about 30μ across, with scalariform thickening.
This plant is similar to Renalia hueberi Gensel in general morphology, but differs
from the latter in possessing root-like and rhizophore-like branches.
The generic name is derived from Prof. Hsü Jen. This paper is a thesis for M. Sc. 相似文献
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《Journal of The Franklin Institute》1929,207(2):273-276
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描述了贵州卷柏属一新种,即习水卷柏Selaginella xishuiensis G. Q. Gou & P. S. Wang。新种与蔓出卷柏S. davidii Franch.在体态和大小方面相近,但叶缘具睫状毛而不同;新种在体态上也与地卷柏S. prostrata H. S. Kung相似,但孢子叶一型而不同。 相似文献
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对中国云南产的兰科新种玲珑兜兰Paphiopedilum microchilum Z．J．Liu et S．C．Chen作了描述和绘图，并简要地讨论了它与彩云兜兰Paph．wardii Summerh．的亲缘关系。 相似文献
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我们学校全体师生齐心协力,锐意进取,从学生最喜欢的活动抓起,从教育最基本的积累开始,关注细节,培育做人做事的品质,努力为学生的一生精彩奠基,取得了积极的成效。 相似文献
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描述了贵州卷柏属一新种,即习水卷柏Selaginella xishuiensis G. Q. Gou & P. S. Wang。新种与蔓出卷柏S. davidii Franch.在体态和大小方面相近,但叶缘具睫状毛而不同;新种在体态上也与地卷柏S. prostrata H. S. Kung相似,但孢子叶一型而不同。 相似文献