Paulownia - Bioenergy Crop Plants - page 673

According to Chinese legend, the mythical phoenix alights only in the branches of the Paulownia
tree when it lands on earth (http://www.onmarkproductions.com/html/ho-oo-phoenix.shtml).
China has historically been the largest grower of Paulownia. Chinese people use its wood for
making furniture, house construction, toys, plywood, musical instruments, and for packaging. For
an ideal multipurpose tree, the Paulownia intercropping models have been applied and extended
to 15 million ha in rural areas of the central plains of north China. The total number of Paulownia
trees growing in China is approximately 1 billion, including those grown as the shelterbelts at the
canal banks and road sides or for ornamental forests around houses and villages. For decades,
Japanese craftsmen have used this revered wood in ceremonial furniture, musical instruments,
decorative moldings, laminated structural beams, and shipping containers. The tree made its way to
the United States in the mid-1800s. Paulownia seeds were used as packaging material for delicate
porcelain dishes on their journey across the Pacific. Once unpacked, the tiny wind-blown seeds
became naturalized throughout the eastern states.
Paulownia also has a unique biological character (i.e., a root system that grows deep and a crown
that develops in loose structure) that makes it suitable for intercropping or in a mixed planting
with other shade-enduring trees. The traditional monocropping models in many of these countries
have been replaced by Paulownia-crop intercropping fields which have resulted in more reasonable
use of sunlight, heat, water, and air resources so that the farmland productivity and the product
diversity are raised. The adoption of Paulownia-crop intercropping is also a good solution to the
land competition between the development of agriculture, forestry, and animal husbandry (Zhu
et al. 1986).
27.3 Botany and dIstrIButIon
Paulownia species are commonly known as Empress tree, Kiri tree, Dragon tree, Royal Paulownia,
Princess tree, and many other derivatives. Paulownia is a genus of between 6 and 17 species
(depending on taxonomic authorities) of plants in the monogeneric family Paulowniaceae, related
to and sometimes included in the family Scrophulariaceae. The Latin name Paulownia was given
by the Swiss botanist Thunberg, and the taxonomic details were published in the “Japanese Flora”
in 1781 (Zhao-Hua et al. 1985). They are native to much of China, southern to northern Laos and
Vietnam, and have long been cultivated elsewhere in eastern Asia, notably in Japan and Korea.
They are deciduous trees 40-50 ft tall, with large leaves 15-40 cm across arranged in opposite
phyllotaxy on the stem. Surface studies of structures present on P. tomentosa suggest that there are
three types of structures that protect young plant parts and/or reproductive organs from herbivores
(Kobayashi et al. 2008). These structures have been named as bowl-shaped organs, glandular hairs,
and dendritic trichomes. Glandular hairs on leaves, stems, and flowers secrete mucilage containing
glycerides and flavonoids and trap small insects. These chemicals seem to play a major role in its
antiherbivore property. The flowers are produced in early spring on panicles 10-30 cm long, with a
tubular purple corolla resembling a foxglove flower. The fruit is a dry capsule containing thousands
of minute winged seeds. The main species in the genus Paulownia are P. tomentosa , P. fortunei ,
P. elongata , P. albiphloea , P. catalpifolia , P. australis , P. kawakamii , and P. fargesii (Zhu et al.
1986). Molecular marker-based studies including random amplified polymorphic DNA (RAPD) and
restriction fragment length polymorphism (RFLP) of chloroplast DNA have been used to establish
the hybrid origin of Paulownia taiwaniana (Wang et al. 1994). This study provided molecular evi-
dence suggesting that P. taiwaniana is the natural hybrid between P. fortunei and P. kawakamii and
that the maternal parent is P. kawakamii .
Paulownia species grow on flat or mountainous land, in various types of soil including rich humus
soil in temperate areas, dry poor soil, rich forest soil, and light clay soil in the subtropics, laterite
soil in the tropics, and dry steppes (semiarid grass covered plains in southeast Europe, Siberia,
central Asia, and Central America). It also adapts to various climates, from warm and temperate
to tropical, and can even withstand temperatures as low as -20°C. Paulownia can survive between