Copyright 1998-2022 Yoshiaki Yoneda

Asagao, the Japanese name for the morning glory, belongs to Convolvulaceae (the morning glory family) in the plant classification. Convolvulaceae, composed of about 50 genera and 1500 species, is distributed across the world's tropical and subtropical regions. Only a small number of species are found in temperate areas. Most species of Convolvulaceae are herbs. The stems of these herbs are twining or prostrate. The flowers are large and funnel-shaped, bell-shaped or crateriform. Many species each have a distinct flower color. Shrubby species are rare and only a few become trees.

The flower has one pistil composed of 2 carpels. The ovary has 2 or 4 locules. (In section Pharbitis of genus Ipomoea, the pistil is composed of 3 carpels and 3 locular ovaries). The flower has 5 stamens. Pollen grains are spheroidal and prolate. Pollen tubues develop from germination colpae or pores.). Most species in many genera, including Convolvulus, have 3 colpae (some species have 4 or 5 colpae-pollen). Calystegia species have ca. 30 pores, while Ipomoea species have 100-200. In the tribes Ipomoeeae and Argyreieae, many spiny protuberances are observed on the outer wall (exine) of the pollen grain. This type of pollen is called the echinate type. In other tribes, such spiny protuberances are not found, so the pollens are called the smooth-surface or psilate type. The fruits are ordinarily dehiscent capsules, while some species have baccate fruits or nut-like fruits.

Convolvulaceae have been studied taxonomically by H. G. Hallier (1893), A. Peter O. R. (1937), S. J. van Ooststroom (1938~43), H. Melchior (1964) and D.F. Austin (1973,1975). The tribe Cuscuteae has special characteristics, including a parasitic life and spiral embryos without cotyledons. It Is therefore sometimes classified as an independent family, Cuscutaceae, separate from Convolvulaceae. Hallier focused on the surface morphology of pollen grains and classified the family Convolvulaceae into two subfamilies: a smooth-surface subfamily, or psiloconiae and a spiny-surface subfamily, or echinoconiae. He considered that the latter would derive from the former phylogenetically. Concerning the number of chromosomes, the tribe Convolvuleae, including the genera Convolvulus and Calystegia, have basic numbers x=10,11,12, while other tribes have x=14,15. Convolvulaceae has been classified according to various criteria, including the morphology of pollen and pistils, the dehiscence of capsules and the chromosome number.

Sanshikihirugao Dwarf convolvulus Convolvulus tricolor	Seiyoohirugao Field bindweed Convolvulus arvensis	Seiyoohirugao Field bindweed Convolvulus arvensis	Seiyoohirugao Field bindweed Convolvulus arvensis
Hirugao Japanese bindweed Calystegia japonica	Kohirugao Japanese bindweed Calystegia hederacea	Hamahirugao Sea bindweed Calystegia soldanella	Husenasagao Operculina turpethum Flower
Husenasagao Operculina turpethum Capsule	Husenasagao Operculina turpethum Dihisced capsule	Baraasagao Wood rose Merremia tuberosa	Baraasagao Wood rose Merremia tuberosa
Tutanohahirugao Merremia hederacea Flower	Tutanohahirugao Merremia hederacea Flower	Kirehahirugao Merremia dissecta Flower	Kirehahirugao Merremia dissecta Leaf
Kirehahirugao Merremia dissecta Capsule	Kirehahirugao Merremia dissecta Matured capsule	Hosobaasagao Merremia tridentata ssp. hastata	Oobaasagao Argyreia nervosa
Oobaasagao Argyreia nervosa Flower	Oobaasagao Argyreia nervosa Leaf	Oobahamaasagao Stictocladia tilifolia	Oobahamaasagao Stictocladia tilifolia
Oobahamaasagao Stictocladia tilifolia	Aoigoke Dichondra repens Leaf	Aoigoke Dichondra repens	Hamanenasikazura Cuscuta chinensis
Hamanenasikazura Cuscuta chinensis Flower

References

1. Clarke, C. B. (1883) Convolvulaceae. In The Flora of British India IV:179 ed. Hooker, J.D.
   
2. Hallier, H. (1893) Versuch einer nat rlichen Gliederung der Convolvulaceen auf morphologischer und anatomischer Grundlage. Bot. Jahrb. Sys. 16: 453-591.
   
3. Peter, A. (1897) Convolvulaceae. In: Natürlichen Pflanzenfamilien IVa:25~31 ed.by A. Engler & Prantl, K.
   
4. Wilson, K. A. (1960) The Genera of Convolvulaceae in the Southeastern United States J. Arnold Arboretum 41:298-317.
   
5. Valentine, D. H. (1972) Convolvulaceae; In Flora Europaea (ed. Tutin, T. G., Heywood, V. H., Burges, N. A., Moore, D. M., Valentine, D. H., Walters, S. M., Webb, D. A.) Cambridge, Univ. Press.
   
6. Austin, D. F. (1973) The American Erycibeae (Convolvulaceae): Maripa, Dicranostyles, and Lysiostyles I. Systematics. Ann. Missouri Bot. Gard. 60: 306-412.
   
7. Austin, D. F. (1975) Family 164.Convolvulceae in Flora of Panama (Woodson, R. E., Jr. & Schery, R.W. & Collabortors) Ann. Missouri Bot. Gard. 62: 157-224.
   
8. Powell, D. A. (1979) The Convolvulaceae of the Lesser Antilles J. Arnord Arbor. 60: 219.
   
9. Yoneda, Y. (1989) Convolvulaceae In: Grand dictionary of horticultural plants vol. 4: 149 (edited by Youtarou Tukamoto). Shougakkan.