Abstract: Diptychocarpus strictus is an early spring ephemeral plant mainly distributed in
Junggar Basin of China. It is one of the few species of Cruciferae that has heterocarpy on the
same raceme. The upper and lower flowers in a raceme develop into two kinds of siliques that
differ in morphology and in manner of dehiscence. This paper deals primarily with the floral
syndromes and breeding system of D. strictus. The results can be summarized as follows. (1)
This species has two floral morphs, purple-flowered and white-flowered, and the color of
flowers is stably inherited. The ratio of the two morphs within a population is close to 1:1. (2)
There are significant differences between the two morphs in anther length of the longer
stamens in the upper part flowers of a raceme and in length of petal and style of the lower
flowers in a raceme (P<0.01). Additionally, there are significant differences between the two
morphs in length of outer sepals, petals, filaments of longer stamens, ovary, and style between
upper and lower flowers in a raceme (P<0.01). The data of morphological characters of the
upper flowers in a raceme are larger than those of the lower flowers. (3) Number of pollen
grains per flower in upper and lower flowers of a raceme in purple-flowered and
white-flowered morphs are 7589.07±976.64 and 5428.93±900.45 and 7044.73±557.37 and
5138.60±813.48, respectively; number of ovules per ovary, 31.83±3.36 and 25.03±3.72
and 32.03±3.43 and 25.70±2.61, respectively; and P/O ratios, 241.31±41.85 and 222.33±
52.51 and 222.19±27.80 and 201.84±37.52, respectively. Number of pollen grains per anther
is greater in the shorter stamens than they are in the longer stamens of the same flower
(P<0.01). Abortion rate of pollen is very low, and it differs between longer and shorter
stamens (P<0.05). (4) In the same raceme of the two morphs, the upper flowers have more
pollen grains, higher P/O ratios, and more ovules than the lower flowers (P<0.01). Also, there
are significant differences between the two morphs in number of pollen grains per anther in
the longer stamens of the upper flowers in a raceme (P<0.01). (5) Pollen longevity and stigma
receptivity barely overlap; the period of highest pollen vigor is just the same as the peak of
stigma receptivity. Dynamic curves of pollen viability of the longer and the shorter stamens in
the two morphs are similar. At the beginning of anther dehiscence, the pollen vigor of both
longer and shorter stamens is >90%. (6) Few pollinators were present during flowering, and
self-pollen could germinate normally on the stigma. In the two morphs, fruit-set was 88.2%
and 85.7%, respectively, in no emasculation and bagging treatments, and 95.0% and 90.0%,
respectively, under conditions of natural pollination, indicating that D. strictus is a facultative
selfer.