|Ravenea is becoming popular again. In the latter part of the 19th century, R.
hildebrandtii was much sought after for the drawing room; nowadays this species is
very rare in cultivation, and our more climatically advantaged members proudly grow their R.
rivularis. Several entrepreneurs are trying to obtain seed of the rare R.
xerophila, which would thrive in rather arid climes. However, the bulk of the genus
is still unknown to the palmeteers' world at large, and that is sad, because there are
some beautiful species as well as some very interesting ones. The genus is restricted, in
the wild, to Madagascar and the Comoro Islands; your editors have described the Comoro
species in this journal (Dransfield and Uhl 1986) and in a recent article I have described
the amazing aquatic Ravenea (Beentje 1993). In 1995, John Dransfield and I hope
to publish "Palms of Madagascar" which will contain full descriptions of the
species, identification keys, and drawings as well as photographs. In this article I'd
like to give you an overview of the genus.
One of the more amazing things about Ravenea is the sheer diversity of the
species. Their habit ranges over a wide spectrum, including small undergrowth palms (R.
hildebrandtii), short and squat palms (R. louvelii), slender middle-sized
trees (R. madagascariensis) and forest canopy giants with bulging trunks (R.
robustior); habitats include dense lowland rain forest where the palm collects litter
(R. albicans), littoral and montane forests (R. sambiranensis), ravines
in rather dry areas (R. glauca), river banks in dry areas (R. rivularis)
and hilltops in arid areas (R. xerophila).
In fact, the genus itself is a member of a closely knit group of genera, the tribe
Ceroxyleae, from a diversity of continents. There is Oraniopsis from Queensland,
Australia; both other members of the tribe grow in South America; there is Juania from
'Robinson Crusoe' (Juan Fernandez) Island, and the Andean wax palms, Ceroxylon,
occur in the high mountains of the Andes.
There used to be a fifth member of the tribe, Louvelia, also from Madagascar;
however, John Dransfield and I have re-found the two most mysterious Louvelia species,
and some intermediates, and it has turned out that there are no true differences between Ravenea
and Louvelia. The two genera form a continuum, with the species at the
opposite ends of the spectrum very different; if just the extremes were known, you would
certainly put them in different genera. But, if you look at the other species, you can
form a chain, of which the links are formed by species which are quite close to each
other-and so you can link the extremes, making this a single genus. Between the bulk of
the genus Ravenea and the other genera of this group, however, there are
differences which cannot be bridged by intermediates. And so it goes.
History of the Genus
One of the main difficulties in the early days of Ravenea taxonomy was the
scarcity of collections and the sex question. Species were described based on one or two
collections, and often from very scrappy ones; this was the reason why early keys to the
species were based on the strangest of characters, such as the keel of the leaf rachis, or
little black hairs on the petiole (probably a fungus). By 1945, when the Flora of
Madagascar and the Comoros was published (Jumelle and Perrier 1945), nine species had been
recognized in Ravenea and three in Louvelia, and all but one of these
have survived my critical revision (Beentje 1994). Several new species have come to light
since 1945. Dransfield and Uhl (1986) described the imposing Ravenea moorei from
the Comoro Islands. John Dransfield found a new species during his field work in the late
1980's, which was intermediate between Ravenea and Louvelia. During my
own field work in Madagascar in 1991 -1993, three more new species came to light, one of
which was described in this journal (Beentje 1993). The main difficulty during my revision
of the genus was the distinction of taxa which are quite close to each other, such as R.
madagascariensis, R. latisecta, and R. sambiranensis. In the field these
seemed quite distinct, but the types, the specimens on which the first descriptions were
based, were scrappy, or even completely missing-such as the type of R. latisecta -
in which case I had to go by the rather hazy published description. The fact that this is
a dioecious genus, with male and female trees, made the identification of scrappy
specimens difficult, and so was the linking of the females with the appropriate males. So
some mysteries remain; probably a good thing, as mysteries are the spice of life!
List of Species
Ravenea albicans (Jum.) Beentje (formerly Louvelia albicans Jum.)
"Hoza-tsiketra" (Fig. 1)
This used to be a Louvelia, as well as a mystery. The type had been collected
by Perrier de la Bāthie in the Masoala Peninsula, but without an exact locality. The date
must have been circa 1925. This species is immediately recognizable by the white underside
to the leaflets (hence the specific name) and a kind of zebra-striping on the leaf rachis.
It should be quite unmistakable in the field-the problem was, which field? None of the
botanists who have collected in the Masoala in recent years had seen it, and this includes
Dransfield, who had searched for it. The original description of 1933 says "common
between Fenerive and Antalaha", casually mentioning an area of some 250 miles of
coastline. After a year of fieldwork I was beginning to despair about this species. Then,
in April 1992, John Dransfield and I were working in a forest near Mananara when John
called out, and started dancing -- he had rediscovered it, ending a sixty-five year old
mystery. It is a 3-6 m tall undergrowth palm with litter-trapping sheath bases and the
typical 'shuttle-cock' crown of many Raveneas. The male inflorescence is hidden among the
sheath bases, but we found a plant in old pistillate inflorescence, and this stuck out
from the sheaths. We still have not seen the fruit, but some seedlings growing under the
tree had the characteristic white under-surface of the leaf. One of the rarest Raveneas,
growing in the wettest rain forests of the country.
Ravenea dransfieldii Beentje "Ovotsarorona"
This species was really the missing link between Ravenea and Louvelia,
and the link was found by John Dransfield on his first trip to Madagascar in 1986. This
medium-sized palm grows in lowland rain forest in eastern Madagascar. It has a hard layer
around the seed as well as the condensed female inflorescence of Louvelia, but
only a single seed per fruit, and a male inflorescence branched to two orders, just as in Ravenea.
So far, it is only known from four sites. Young leaves are used for making high-quality
Ravenea glauca Jum. & H. Perrier "Sihara" (Figs. 3,4)
A very graceful palm, which would probably do quite well in cultivation; in the wild,
it occurs along streams and in ravines in the drier (but not arid) parts of
southern-central Madagascar. The trunk is slender, the crown consists of 14-20 slightly
arching leaves, and the leaflets have a slightly waxy layer on the underside, which gives
the species its name. I have seen it growing on sandstone wars of ravines, in tiny cracks,
but also in dry sandy riverbeds; both sites seemed quite dry, but probably get wet at
intervals. The original description reports vast forests of this species in the
Andringitra Mountains of central-southern Madagascar (again, on their drier slopes),
without any undergrowth. I find this hard to believe, but ....