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A Study on the Pollen Morphology in Trochodendron, Tetracentron and Euptelea

Wang Fu-Hsiung, Chien Nan-Fang, Zhang Yu-Long   

  1. (Institute of Botany,  Academia Sinica,  Beijing)
  • Received:1900-01-01 Revised:1900-01-01 Online:1984-12-18 Published:1984-12-18
  • Contact: Wang Fu-Hsiung

Abstract:

Trochodendron,  Tetracentron and Euptelea are considered as a small
group of the primitive angiosperms. They are endemic to or mainly distributed in China.
Their systematic position has long been debated. The purpose of the present work is to
present palynological data both for systematic discussion and for the identification of
fossil pollen.
     The three genera share a number of pollen characters,  for example,  being spheroid
in shape,  exine surface distinctly reticulate and lumina rather small and irregular in
shape,  etc.  They are,  however,  obviously different in other respects of pollen morphol-
ogy. The pollen grains of Euptelea are the largest of three (c. 30 μm in diameter),  those
of Tetracentron,  the smallest (c. 15) and those of Trochodendron,  intermediate (c. 20),  
3-colpate in Trochodendron and Tetracentron,  and those in Euptelea are 3-celpate but
with transitional apertures in one species and 6-rugate,  not 3-colpate,  in the other. The
ruga membranes are coarsely granular (rod-shaped elements under SEM).  The lumina
are the smallest in Euptelea. Muri in Tetracentron are distinctly striate.  Thus,  the es-
tablishment of three separate families is supported by pollen morphology.
     Since the pollen grains of Trochodendron and Tetracentron are 3-colpate and those
of Magnoliaceae are 1-sulcate,  it seems unreasonable to refer them to Magnoliaceae (or
Magnoliales).  If the rugae of pollen grains in Euptelea further shortened and their
number increased,  they would resemble those of Hamamelidaceae (such as Sycopsis).
Pollen morphology,  therefore,  suggests that Euptelea is related to Hamamelidales,  and
supports Cronquist’s viewpoint.  Hutchinson (1969) includes both Trochodendron and
Euptelea in the same family (Trochodendraceae). However,  these two genera are rather
distinct in morphology and structure,  the presence or absence of vessels and chromosome
number,  etc.  Pollen morphology of two genera also disagrees with the Hutchinson’s
viewpoint.

Key words: Trochodendron, Tetracentron, Euptelea, pollen morphology

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