IANKESTERIANA2 19-21 2001


 THE GENUS CHRISTENSONIA HAAGER


 ERIC A. CHRISTENSON

 1646 Oak Street, Sarasota, Florida 34236, U.S.A.


ABSTRACT. The monotypic Vietnamese genus Christensonia Haager is discussed and illustrated by a
detailed line drawing. A warm-growing, lowland plant, C. vietnamica is an exciting addition to the
tropical horticulture as well as a taxonomic bridge between the genera Aerides, Rhynchostylis, and
Vanda.

RESUMEN. Se discute y se ilustra con un dibujo de plumilla detallado el g6nero monotipico vietnami-
ta Christensonia Haager. Una plant de clima calido, native de tierras bajas, C. vietnamica es un
interesante aporte a la horticulture tropical, asi como un puente taxon6mico entire los g6neros
Aerides, Rhynchostylis y Vanda.

KEY WORDS: Orchidaceae, Aeridinae, Christensonia, Christensonia vietnamica, Vietnam


 In 1993 Czech botanist Jiri (George) Haager
kindly honored me by describing a new genus of
Vietnamese orchids Christensonia (Haager 1993).
In that account and later mention of the genus
(Christenson 1996), space consideration did not
allow publication of an excellent line drawing of
the type plant by Haager. This article rectifies this
situation.
 A member of the subtribe Aeridinae (synonym:
Sarcanthinae), Christensonia exhibits a mosaic of
characters found in the closely related genera
Aerides Loureiro, Rhynchostylis Blume, and Vanda
Jones.
 Christensonia differs from Aerides by having no
column foot. And unlike most species of Aerides,
the lip of Christensonia is not flexibly hinged
below the lateral lobes allowing deflexion of the lip
by pollinators. Christensonia is similar to
Rhynchostylis, especially in having a narrowly lin-
ear stipe to the pollinarium, but differs by having a
clearly three-lobed lip. In addition, plants of
Christensonia are miniature and few-flowered
compared with Rhynchostylis.
 Christensonia is perhaps most similar to Vanda.
In particular, Christensonia shares two characteris-
tics with Vanda. First, the spurs are straight and in
the same plane as the midlobe of the lip. Second,
the only flexible portion of the lip is the base of the
midlobe.


 The green and white flowers of Christensonia
are unlike the generally white and rose-purple pat-
terns seen in Aerides and Rhynchostylis. However,
they are similat to some species of Vanda, especial-
ly those of Vanda section Cristatae Lindley which
are sometimes segregated as the genus Trudelia
Garay (q.v., Christenson 1994). Nothing is known
of the pollinaton biology of Christensonia nor the
significance, if any, of the green and white floral
coloration.
 Plants of Christensonia have entered horticul-
ture and are readily available commercially in the
United States. A plant cultivated in Sarasota,
Florida, for several years has proven to be vigorous
and trouble-free to grow. Its first flowering was on
a plant of the similar size to the one shown in the
drawing. Plants in the Czech Republic and the
United States flower in july. Its flowering season in
nature is unknown.

Christensonia vietnamica J.R. Haager, Orchid
Digest 57(1): 40. 1993.

 TYPE. Southern Vietnam, Prov. Khanh Hoa,
Ninh Tay village, 100 m, April 1989, collected by
0. Dubec and J. Jurak, flowered in cultivation in
Prague, PR 11392 holotypee, PR). FIG. 1.

 Monopodial epiphytes. Stems to 30 cm long.
Leaves strap-shaped, erose at apex, to 6 x 1 cm.