Pachypodium bicolor

Pachypodium bicolor
Scientific classification
Kingdom:	Plantae
Clade:	Tracheophytes
Clade:	Angiosperms
Clade:	Eudicots
Clade:	Asterids
Order:	Gentianales
Family:	Apocynaceae
Genus:	Pachypodium
Species:	P. bicolor
Binomial name
	Pachypodium bicolor; Lavranos and Rapanarivo

Pachypodium bicolor is a species of plant in the family Apocynaceae.

The species has a

habit of a low growing somewhat pendulant shrub with a thickened trunk and a densely branched crown

composed of numerous branches.

It has been elevated from a "forma" taxonomical ranking of Pachypodium rosulatum variety rosulatum forma bicolor to a full species by Lavranos and Rapanarivo in 1997. A "forma" is a specific taxonomic ranking below subspecies and usually designates the smallest degree in taxonomical nomenclature recording the slightest difference between taxa, typically based on one chief character. It chief character that distinguishes Pachypodium bicolor from other species with yellow

corolla is the presence of a white corolla tube or throat to the flower. Pachypodium bicolor is part of the Pachypodium rosulatum complex, where discussion centers on rather one is dealing with one species with many varieties, as Gordon Rowley argues, or many separate distinct species. The corolla, the collective term for the petals of a flower or the inner whorl of the perianth

, in the nexus for taxonomical confusion of the taxon.

Pachypodium bicolor is

Cultivation should stimulate

this substrate.

It does not have a common name in the native tongue to Malagasy—from Madagascar.

Morphology

Habit

Pachypodium bicolor is a

conical

at 0.6 to 0.75 times the spine length. The young spines and the base of young leaves are densely white-lanate, having or consisting of woolly hairs.

Leaves

The

costa, with tertiary—third level of —venation

reticulate, composing or a pattern of a netting.

Inflorescence

The

pubescent

, hairy outside and sparsely pubescent inside.

Flowers

Collectively forming the outer

pubescent, hairy outside and glabrous, smooth without hairs inside. The sepals are acuminate, tapering gradually to a sharp point at the tips of certain leaves or petals or sepals

, at their apex.

Corolla

The

obovate

at 0.6 to 0.8 times as long as the tube. That measures at 1.2 to 1.5 times as long as wide, or 1.5 by 1.0 to 1.2 cm (0.59 by 0.39 to 0.47 in). The lobes are rounded at their individual apex.

Stamens

The

anthers are 7 to 8 mm (0.28 to 0.31 in) by 1 mm (0.039 in). The anthers have stiff hairs at the base of the connective, the sterile

part between just below where they occur with the pistil head.

Pistil

The

carpel

, one of the structural units of a pistil, representing a modified, ovule-bearing leaf.

Fruit

The

pubescent

with short hairs. The fruit wall is approximately 0.5 mm (0.020 in) thick.

Seeds

The

cotyledons, the leaves of the embryo of a seed plant, are ovate, oval, egg-shaped, at 1.22 to 1.83 times as long as wide, measuring, 2.2 mm by 1.2 mm to 1.8 mm (0.09 in by 0.05 to 0.07 in). They are rounded at the apex and subcordate, somewhat like a heart in shape, at the base. The rootlet that forms is 1.04 times as long as the cotyledons

at 2.3 mm long by 1 mm by 1.5 mm (0.09 by 0.04 by 0.06 in).

Habitat

Distribution

Distribution to Madagascar. East of Belo sur Tsiribihina.

Habit

Partly pendulant, Pachypodium bicolor forms a low shrub with a thickened trunk and a densely branched crown, the upper part of a tree or shrub, which includes the branches and leaves.

Ecology

Pachypodium bicolor is positioned on porous

Orchids sp. (0.09 by 0.04 inch) and Kalanchoe

spp. (Crassulaceae).

Cultivation

Based on W. Röösli within Rapanarivo et al. "Cultivation"

The substrate should be loose peat with quartz sand at a pH level of 4.5. Temperatures from spring to autumn: night 20 °C (68 °F) to day 40 °C (104 °F). Wintertime and dormancy: night 16 °C (61 °F) and day 20 °C (68 °F). It flowers in the spring, presumably after dormancy, so it needs very dry conditions during its dormancy with only occasionally a little water.

Reproduction

By seeds or cuttings.

Literature

Again, in 1997, Pachypodium bicolor was given a full species level by the botanists J.J. Lavranos and S.H.J.V. Rapanarivo in the "Cactus and Succulent Journal" 69: 29-32 (1997).

Its species type is: Madagascar, Toliara, along the Tsiribihina River, Bekinankina, West of Berevo, W. Röösli and R. Hoffman 33/96 (holotype P; isotype MO, TAN, WAG, ZSS). Fig 2, p. 15; Map 2, p. 12; Plates 5-7, opposite p. 17.

G.D. Rowley apparently disagrees with this species definition and maintains another taxonomical ranking altogether in two of his works covering this issue of the taxon, visible in: Homotypic synonym Pachypodium rosulatum variety rosulatum forma bicolor (Lavranos & Rapanarivo) G.D. Rowley in Bradleya 16: 107 (1998) and Pachypodium & Adenium, The Cactus Files Handbook 5: 57 (1999), syn. nov

So what the reader can make of this taxonomical situation is that there is still considerable debate by very skilled botanists.

This article maintains the species rank of Pachypodium bicolor because of the presence of a white throat, or the

corolla tube, is consistent with the authors of the most recent book to undertake a widespread examination of Pachypodium in situ, or in the landscape, of continental southern Africa and Madagascar. Furthermore, the taxonomical definition of the taxa

as a species has been accepted with the public use of the taxonomical rank, Pachypodium bicolor apparently.

References

Rapanarivo, S.H.J.V., Lavranos, J.J., Leeuwenberg, A.J.M., and Röösli, W. Pachypodium (Apocynaceae): Taxonomy, habitats and cultivation "Taxonomic revision of the genus Pachypodium," S.H.J.V. Rapanarivo and J.J. Lavranos; "The habitats of Pachypodium species" S.H.J.V. Rapanarivo; "Cultivation" W. Röösli. (A.A. Balkema: Rotterdam, Brookfield, 1999) [The rest of the list is based on Rapanarivo et al.]
Rowley, G.D. "The Pachypodium rosulatum aggregate (Apocynaceae) - one species or several?" Bradleya: The British Cactus and Succulent Society Yearbook. (16/1998)