Abstract:

This paper reports the bisexual structure of the flowers of Pterocarya

stenoptera. The bisexual flowers are borne at the end of a leafy shoot of the current year

in many-flowered terminal pendulous catkins. They have the same structure as the general

female ones. Each flower grows in the axil of a bract,  with a pair of bracteoles and four

small perianths. Each flower has two or three carpels in the centre of the flower,  and upon

them there are two or three styles with stigmas on the inner face. They differ from the ge-

neral female ones in that each of them contains 4-6 stamens,  forming a single whorl. The

stamens alternates with,  or is opposite to,  the perianth elements. Sometimes they contain

8 (-10) stamens,  forming two whorls,  with 6 in the outer whorl and 2 (-4) in the in-

ner whorl, and in this case the pistil in the bisexual flower of terminal catkins often becomes

a rudiment.

      It is interesting that we have also found bisexual flowers in another tree,  which are

borne in lateral male catkins. They have the same structure as general male ones,  and the

pistils are often represented by a rudiment.

      Manning (1940) points out that some female flowers of Pterocarya stenoptera and P.

fraxinifolia occasionally have stamens ( ? ) opposite the sepals. In P. stenoptera we have found

that both the stamens and the stigmas of bisexual flowers are functional. They are capable

of producing functional fruits. This is the same case as in Myrica Gale described by Davey

and Gibson (1917). Rendle (1952) points out that in the male flowers of Platycarya the

pistils often appeared as a rudiment. He considers,  however,  the male flowers derived from

the bisexual flowers with an indefinite number of stamens. The rudimentary pistils of later-

al male catkins in P. stenoptera we found are just the same as the ones found in Platycarya

by Rendle.

      The discovery of the bisexual flowers in P. stenoptera may prove that the unisexual

flowers of the present-day Juglandaceae are derived from ancestors with bisexual flowers.

This tends to support the hypothesis that Cycadicae is the possible ancestor of the angiosperms.

Key words: Juglandaceae, Pterocarya stenoptera, bisexual flowers