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{{Taxobox
| color = lightgreen
| name = ''Pachypodium bicolor''
| regnum = [[Plantae]]
| divisio = [[Flowering plant|Magnoliophyta]]
| classis = [[Magnoliopsida]]
| ordo = [[Gentianales]]
| familia = [[Apocynaceae]]
| genus = ''[[Pachypodium]]''
| species = '''''P. bicolor'''''
| binomial = ''Pachypodium bicolor''
| binomial_authority = Lavranos and Rapanarivo
}}

'''''Pachypodium bicolor''''' belongs to the ''Dogbane'' family [[Apocynaceae]], now merged with the "Milkweed" family [[Asclepiadaceae]], a move with great [[botany|botanical]] implications to succulent enthusiasts.

The species has a [[Plant habit|habit]] of a low growing somewhat pendulant [[shrub]] with a thickened [[trunk]] and a densely [[branch|branched]] [[Crown (botany)|crown]] composed of numerous branches.

It has been elevated from a "forma" [[taxonomy|taxonomical]] ranking of ''Pachypodium rosulatum'' variety ''rosulatum'' [[form|forma]] ''bicolor'' to a full [[species]] by Lavranos and Rapanarivo in 1997. A "forma" is a specific taxonomical 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 varieities, as Gordon Rowley agrues, or many separate distinct species. The corolla, the collective term for the [[petal]]s of a [[flower]] or the inner whorl of the [[perianth]], in the nexus for taxonomical confusion of the taxon.

''Pachypodium bicolor'' is [[endemic (ecology)|endemic]] to [[Madagascar]] in the low, open, [[deciduous]], western [[forest]] growing on porous [[sandstone]]. Again, it should be noted that the [[geology|geological]] preference of ''Pachypodium bicolor'' is limited to one [[Substrate (biology)|substrate]], thus making it geological preference more [[specialized]] to an [[natural environment|environment]]. [[Cultivation]] should [[stimulation|stimulate]] this substrate.

It does not have a [[common name]] in the [[wiktionary:native|native]] tongue to [[Malagasy]]--''from Madagascar.''

==[[Morphology (biology)|Morphology]]==
===Habit===

''Pachypodium bicolor'' is a [[succulent]] [[plant]], as are all ''[[Pachypodium]].'' It grows normally 25 cm to 50 cm (10 to 20 inches) in height with a densely branched [[Crown (botany)|crown]] that is up to approximately 50 cm (20 inches) broad in diameter. Each [[branch]] is cylindrical and measures 6 cm to 14 cm (2.4 in to 5.5 inches) in diameter at the base. The branch comes from low down on the base of the plant. The branches are covered with [[leaf]] [[scar]]s and the remains of [[spine (biology)|spines]]. Beyond their base, the branches measure 3.5 cm (1 3/8 inches) in diameter. Pale-grey in color, the [[bark]] is smooth. [[Branch]]lets from 1.5 cm to 5 cm (0.6 to 2 inches) long and 8 mm to 12 mm (1/3 to 1/2 inches) in diameter. They are covered with paired straight grey-brown spines 2 mm to 8 mm (0.08 to 0.3 inches) long and 1.0 mm to 3.5 mm (0.04 to 0.14 inches) in diameter at the base. The [[anatomical terms of location|basal]] part, located at or near the base of a plant stem, is part of the spine and [[cone (geometry)|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 [[leaf|leaves]] of ''Pachypodium bicolor'' are subsessile, very much [[stalk (botany)|stalkless]] and attached directly at the base of the leaf, and confined to the [[apex|apices]] of the [[branch]]lets. The leaves can be [[Petiole (botany)|petiole]], having a stalk by which a leaf is attached to a [[Plant stem|stem]], at 0 mm to 2 mm (up to 0.08 in) long; meaning they have a very short stalk to the leave, if at all. [[Pubescent]]—hairy—the leaf [[blade]] is medium green with a pale green midrib above and a pale green below along with reticulate [[veins|venation]] beneath when fresh. When the leaves are dried they are papery. Geometrically they take the shape of being [[ovate]], shaped like an egg, to [[ellipse|elliptic]] or narrowly elliptic at 3 to 5 times as long as wide. That measures at 3 cm to 7.5 cm (1¼ to 3 in) long by 0.8 cm to 2 cm (0.3 to 0.8 in) wide. At the apex, the blade is obtuse, having a blunt or rounded tip; to [[rounded]]; and [[cuneate]], wedge-shaped or triangular; at the base; glabrous, smooth; and with impressed [[veins|venation above]]; ciliolate—''having minute hairs along the [[margin]] or edge of a [[structure]]''. Beneath the blade is [[pubescent]] beneath, with 14 to 40 pairs of rather straight secondary [[veins]] forming an angle of 45–90° with the [[Glossary of Lepidopteran terms|costa]], with tertiary—''third level of ''—[[vein|venation]] reticulate, composing or a pattern of a netting.

===[[Inflorescence]]===

The [[inflorescence]] is of ''Pachypodium bicolor'' is pedunculate, having the [[stalk (botany)|stalk]] of an inflorescence. It is congested at 15 cm to 30 cm (6 to 12 in) by 6 cm to 9 cm (2¼ to 3½ in) with 5 to 8 flowers. The peduncle, the stalk, is terete, [[cylindrical]] but usually slightly tapering at both ends, circular in cross-section, and smooth-surfaced. It measures 120 mm to 250 mm (4¾ to 10 in) by 2 mm to 4 mm (0.08 to 0.16 in). The [[pedicel]]s, small stalk or stalk-like parts bearing a single flower in an inflorescence, are pale reddish-green at 12 mm to 17 mm long (1/2 to 2/3 in). They are slightly elongated in fruit at 2.3 cm (0.9 in). The [[bract]]s are pale green, persistent—''lasting until the [[maturity]] of the flower''—and narrowly oblong, having a somewhat elongated [[spherical]] form with approximately parallel sides. They measure 4 mm to 6 mm (0.16 to 0.26 in) by 1 mm (0.04 in) and [[pubescent]], hairy outside and sparsely pubescent inside. 

====Flowers====

Collectively forming the outer [[floral]] [[envelope]] or layer of the [[perianth]] enclosing and supporting the developing [[bud]], which is usually green; the [[sepal]]s, are pale green, narrowly [[ovate]]—''oval or egg-shaped''—and 2 to 3 times as long as they are wide, measuring at 3 mm to 5 mm (0.12 to 0.2 in) by 1 mm to 2 mm (0.04 to 0.08 in). They are [[pubescent]], hairy outside and glabrous, smooth without hairs inside. The sepals are acuminate, tapering gradually to a sharp point at the tips of certain [[leaf|leaves]] or [[petal]]s or [[sepal]]s, at their [[apex]].

====Corolla====

The [[corolla]], a collective term for all the [[petal]]s of a [[flower]], is limb and medium yellow outside and bright yellow inside for ''Pachypodium bicolor''. The corolla is pale green at the base, medium yellow outside with 5 very pale green lines to just below the [[lobe]]s. The distinguishing character of ''Pachypodium bicolor'' is that its throat or the inside of the [[corolla]] [[tube]] is white for about 3.5 cm long in the mature bud. It forms a broadly [[ovoid]] head 0.3 of the [[bud]] length in comparison, measuring at 10 mm by 8 mm (0.4 by 0.3 in). Obtuse at the apex, it is [[pubescent]], hairy outside and glabrous, smooth on the part of the lobes covered in bud. The pubescent belt inside is 2 mm (0.08 in) wide just below the insertion of the stamens. The corolla tube is [infundibuliform, or more simply [[funnel]]-shaped, at 5 to 10 times as long as the [[calyx (botany)|calyx]]—''the outer most layer of leaves in a flower, which are often green.'' The calyx is 1 to 1.46 times as long as the lobes at 2.5 cm to 3 cm (1.0 to 1.2 in) long. The basal part of the tube is almost [[cylindrical]] at 0.18–0.22 of the length of the entire tube, or 3 mm to 4 mm (0.12 to 0.16 in) long by 2 mm to 3 mm (0.8 to 0.12 in) wide. Towards the slightly widened apex, the upper part of the tube is obconical, inversely conical, at base and almost cylindrical above measuring at 21 mm to 27 mm (0.8 to 1.1 in) long to 8 mm to 12 mm (0.3 to 0.5 in) wide at the mouth. The lobe at the [[apex]] of the corolla tube are [[oblique]]ly [[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 cm to 2 cm (0.6 to 0.8 in) by 1.0 cm to 1.2 cm (0.4 to 0.5 in). The lobes are [[rounded]] at their individual apex.

====Stamens====

The [[stamen]]s, the [[male]] [[reproductive]] [[organ (anatomy)|organ]] in a flower, have an [[apex]] 15 mm to 16 mm (0.59 to 0.63 in) below the opening, or mouth, of the [[corolla]] tube. They are, therefore, inserted at 0.16 to 0.2 of the length of the corolla tube. That measures at 5 mm to 6 mm (0.20 to 0.24 in) from the base. The [[anther]]s are 7 mm to 8 mm (0.28 to 0.32 inch) by 1 mm (0.04 in). The anthers have stiff [[hair]]s at the base of the [[connective]], the [[infertility|sterile]] part between just below where they occur with the pistil head.

====Pistil====

The [[pistil]], the [[female]] reproductive part of a flower, is 7 mm to 8.5 mm (0.28 to 0.33 in) long. The [[ovary (plants)|ovary]] 2 mm long by 2 mm wide by 1.5 mm high (0.08 mm by 0.08 mm by 0.06 mm). They are [[pubescent]] or sparsely so with short, straight hairs. The [[disk]] of 5 unequal [[gland]]s has 2 glands or 2 pairs of glands that are partly or entirely fused. These glands are broadly [[ovate]], oval or egg-shaped, at 1 mm (0.04 in) high, rounded, [[margin|emarginate]] or obtuse with an irregularly toothed [[apex]] that is less than half as long as the ovary. The [[carpel|style]] is filiform, having the form of or resembling a thread or filament, where it gradually thickens into a cylindrical-head. Composed of an obconical—''inversely conical—''basal part 0.6 mm by 0.7 mm (0.02 by 0.03 in), the pistil head is 1.2 mm (0.05 in) high. It has a ring-shaped central part 0.4 mm by 0.8 mm (0.016 by 0.032 in) with a stigmoid [[apex]] measuring 0.2 mm by 0.4 mm (0.008 by 0.016 in). The ovules are approximately 50 in each [[carpel]], one of the structural units of a pistil, representing a modified, ovule-bearing leaf.

===Fruit===

The [[fruit]] of ''Pachypodium bicolor'' is composed of 2 separate mericarps, sometimes only developing one. Mericaps are a carpel with one seed or one of a pair split apart at [[maturity]]. They form an angle from 10–60° at the base. Worth mentioning, there are occasion when the [[flowers]] and fruit in the same [[inflorescence]]. The mericarps are pale brown with [[longitudinal]] lines outside. Inside it is whitish inside and fusiform, tapering at each end; spindle-shaped, at 60 mm to 100 mm (2½ to 4 in) by 3 mm to 6 mm (0.12 to 0.24 in). The mericarps are acute, having a sharp point or tip, at the apex and are [[pubescent]] with short hairs. The fruit wall is approximately 0.5 mm (0.02 in) thick.

===Seeds===

The [[seed]]s are pale to medium brown, [[ovate]], oval, elliptic, elliptical at 5 mm wide by 2 mm (0.2 by 0.08 in). The [[margin]] is revolute towards the hilar side. In other words, the edge of the seed is rolled backward from the margins to the undersurface on the scarred side of the seed from a [[stalk (botany)|stalk]] connecting an [[ovule]] or a seed with the [[placenta]]. The testa, the often thick or hard outer coat of a seed, is rough. The [[embryo]] is 4.5 mm (0.18 inch) long. 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 [[root]]let that forms is 1.04 times as long as the [[cotyledon]]s at 2.3 mm long by 1 mm by 1.5 mm (0.09 by 0.04 by 0.06 in).

==[[habitat (ecology)|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 (botany)|crown]], the upper part of a tree or shrub, which includes the branches and leaves.

===Ecology===

''Pachypodium bicolor'' is positioned on porous [[sandstone]] where it grows only in full [[sunlight]]. With an emphasis on openness, it is found in low open [[deciduous]] Western [[forest]]. It grows at about an [[altitude]] of approximately 30 m (100 ft). The limitation to one [[Substrate (biology)|substrate]], a low altitude in the landscape, suggests that ''Pachypodium bicolor'' has developed a specialized landscape-[[natural environment|environmental]] condition that should affect its [[horticulture]]. Other plants that can be found around it, species indictors, are ''[[Euphorbia]]'' aff. ''pedilanthoides'', ''E. viguieri'' (Euphorbiaceae), ''Uncarina leandrii'' var. ''rechbergeri'' (Pedaliaceae), ''[[Aloe]]'' sp., (Asphodelaceae) (Orchidaceae)(0.09 by 0.04 inch''[[Orchids]]'' sp.(0.09 by 0.04 inchand [[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 [[holotype|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 [[taxonomy|taxonomical]] ranking altogether in two of his works covering this issue of the taxon, visible in: ''[[homotype|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 wide-spread examination of ''[[Pachypodium]]'' ''in situ'', or in the landscape, of continental [[southern Africa]] and [[Madagascar]]. Furthermore, the taxonomical definition of the [[taxon|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)

{{pachypodium}}

[[Category:Apocynaceae]]
[[Category:Flora of Madagascar]]

Pachypodium bicolor - Revision history

MediaWiki default at 05:14, 30 September 2007