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A Study on the Morphology of Foliar Trichomes of Evergreen Oaks (Quercus) in China and Its Implication in Taxonomy

Liang Hong-Ping, Jen Hsien-Wei, Liu Yi-Qiao   

  • Received:1900-01-01 Revised:1900-01-01 Online:1990-03-10 Published:1990-03-10
  • Contact: Liang Hong-Ping

Abstract:

Most of the evergreen oaks (Quercus L.) are endemic to China and distributed in a
large moutainous area of southwestern China at an altitude of 2600-4000m. The delimitation
of sections and species in the group has not been satisfactorily solved.
      The foliar trichomes are very an important character in identifying species of oaks. As  a
result of observation on 17 species and 2 varieties of evergreen oaks in  China under scanning
electron microscope, ten types of foliar trichomes are recognized: Simpleuniseriate, Simple-br-
anched, Bulbous, Rosulate, Solitary, Stipitate-fasciculate, Fasciculate, Multiradiate, Stellate and
Fused-stellate. The first four types fall into glandular trichomes and the last six non-glandular
trichomes. The taxa examined have a combination of various types of the trichomes.  All the ev-
ergreen oaks have non-glandular trichomes on their foliar epidermis, but glandular trichomes
occur solely in certain taxa. These two types of foliar trichomes are obviously different in stru-
cture and function, which represent different adular trichomes and the last six non-glandular
en oaks are divided into two groups: the glandular group and the non-glandular group accord-
ing to the types of foliar trichomes and it is reasonable to divide the evergreen oaks into two sec-
tions: Sect. Suber (Reichenb.) Spach and Sect. Englerianae (A. Camus) Hsu et Jen.
      Foliar trichomes of the evergreen oaks show a continuity in density from species predom-
inately with glandular trichomes at a high altitude to species solely with non-glandular trichom-
es at a low elevation. The characters of branching of foliar trichomes, especially the number of
branches, can imply to some extent the evolutionary position of a given evergreen species. Consi-
dering the types, density and branches of foliar trichomes combined the evolutionary relation-
ships among the evergreen oaks in China are proposed. Q. gilliana is the startpoint, from where
evolution took place in two directions: glandular and non-glandular. In the glandular direc-
tion envolved are Q. aquifolioides, Q. longispica and Q. guyavaefolia.  Q. pannosa is a species
with the most types and highest number of glandular trichomes.  In non-glandular line aligned
are Q. spinosa, Q. senescens, Q. senescens var. muliensis, Q. monimotricha with the reduction of
glandular trichomes and increase of non-glandular trichomes. After Q. tungmaiensis no glandu-
lar trichomes appear and it solely depends on non-glandular trichomes to protect itself. Q. gran-
chetii is the climax in the non-glandular line with the highest  density and number of bran-
ches of foliar trichomes. And then some species, such as Q. engleriana, Q. phillyraeoides, have
few or no trichomes. Q. dolicholepis, Q. baronii and Q. baronii var. capitata show the close re-
lationships because they share fused-stellate trichomes.

Key words: oak, foliar trichome

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