NOVON 12: 433–436. 2002. Volume 12 Number 4 2002 NOVON Diplopanax vietnamensis, a New Species of Nyssaceae from Vietnam—One More Living Representative of the Tertiary Flora of Eurasia Leonid V. Averyanov Komarov Botanical Institute of the Russian Academy of Sciences, Prof. Popov str., 2, St.-Petersburg, 197376, Russia. av@herb.bin.ras.spb.ru Nguyen Tien Hiep Institute of Ecology and Biological Resources of the National Center for Natural Sciences and Technology of Vietnam, Nghia Do, Cau Giay, Hanoi, Vietnam ABSTRACT. A new species of Diplopanax, D. viet- namensis (Nyssaceae, Cornaceae s.l.), was discovered in the mountains of southern Vietnam. It differs from the single known species, Diplopanax stachyanthus, by short, simple, densely pubescent inflorescences and large yellow-white flowers with five prominent bosses on the flower disc. This genus (with two spe- cies, D. stachyanthus and D. vietnamensis) is now re- garded as congeneric with Mastixicarpum, represen- tatives of which were an integral component of the Mastixia-like paratropical broad-leaved evergreen vegetation that covered much of the Northern Hemi- sphere from the uppermost Cretaceous to the late Mio- cene, about 65 to 7 million years ago. Key words: Diplopanax, Nyssaceae, Tertiary flora of Eurasia, Vietnam. The montane flora within the eastern part of the Indochinese Peninsula is still relatively unknown. Without a doubt it is diverse and conceals a great number of exciting discoveries. Floristically, the highland forests of this area represent relictual remnants of a primitive, tropical flora that occupied wide tropical and subtropical areas of Europe, Asia, and North America during the early Tertiary, ap- proximately 40–70 million years ago (Axelrod et al., 1998; Kubitzki & Krutzsch, 1998; Zhang & Lu, 1998). Due to subsequent climate cooling and in- creased aridity, the European and North Asian rep- resentatives of this highland tropical flora and its corresponding climatic zone have disappeared al- most completely. Small relictual and depauperate elements of it can still be found in Portugal, the Colchis, and in a few other orographically favored continental regions. The largest remaining humid warm Tertiary flora was shifted to Southeast Asia. One of the richest assemblages of ancient, tropical Tertiary taxa may now be observed in highland trop- ical areas of Southeast Asia. Primary mountain for- ests of this region include a surprisingly large pro- portion of archaic genera well represented in the fossil record of the Upper Cretaceous and Lower Ter- tiary recorded from Europe, East Asia, and North America (Kubitzki & Krutzsch, 1998; Martinetto, 1998). Among them are numerous Actinidiaceae, Annonaceae, Berberidaceae, Chloranthaceae, Daphniphyllaceae, Fagaceae, Hamamelidaceae, Jug- landaceae, Lardizabalaceae, Lauraceae, Magnoli- aceae, Menispermaceae, Nyssaceae, Pentaphylaca- ceae, Platanaceae, Ranunculaceae, Rhoipteleaceae, Sabiaceae, Saururaceae, Theaceae, as well as a num- ber of gymnosperm genera such as Amentotaxus Pil- ger (Cephalotaxaceae), Cephalotaxus Siebold & Zuc- carini ex Endlicher (Cephalotaxaceae), Glyptostrobus Endlicher (Taxodiaceae), Keteleeria Carrie `re (Pina- ceae), Pseudolarix Gordon (Pinaceae), and a great number of others (Axelrod et al., 1998; Martinetto, 1998; Nguyen, 1998; Nguyen & Nguyen, 1998; Wu