J Syst Evol ›› 1982, Vol. 20 ›› Issue (3): 331-342.
• Research Articles •
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 pseudomonopodially and bearing dichotomous lateral branches which somewhat differentiate into vegeta,
tire and fertile ones, with dichotomous root-like and rhizophore-like appendages. Sporangia terminal, round to reniform or wide reniform, dehiscing along distal margin into
two equal halves. Spores homosporous, trilete. Stomata anomocytic. Protostele centrarch.
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 arising 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. Rootlike 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 diameter. 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.
Li Cheng-Sen. Hsüa robusta, a new land plant from the Lower Devonian of Yunnan, China. J Syst Evol, 1982, 20 (3): 331-342.
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