Pachypodium saundersii

Pachypodium saundersii is a member of the same family as Adenium and Plumeria (frangipani), the Apocynaceae or Dogbane family.  This species is a hardy, fast grower, that will flower at a small size (12") and a young age (1 year).  Its growth habit is a low branching caudiciform, flowering at the apex of this year's growth, usually in late summer or fall.  The shiny white flowers occur in clusters, each flower lasting a couple of days, but the flowering time can be several weeks.  The stems of this Pachy can get to over a foot across in only a few years if given good conditions.  They are strong summer growers and will usually go dormant if allowed to go below about 50 degrees or so.  (This is how I grow mine.)  They are not damaged until the temperatures dip into the 20's.

The 1 1/2-2" diameter flowers are easily hand pollinated using the typical moth mimicking technique, but are often pollinated by our resident hawk or sphinx months.  This plant was pollinated in this way, and I think way more effective than if I had attempted it.  In this family the fruits (called follicles) are produced in pairs.  Each fruit may contain several dozen seeds, most of which will germinate if sown during the peak of summer.  As seen in the following two images, the seed is designed for wind dispersal.

P. saundersii makes a great potted specimen with natural 'bonsai' like growth.  The long branches can be cut back to maintain a more compact form.  When grown in full sun, summer watering should be ample, and rapid growth will take place in larger pots.  Mature specimens can be under-potted for effect. 
Pachypodium saundersii was named for a botanist who first collected it in South Africa in the late 1800's. 'Pachypodium' means 'thick foot', referring to the thickened stem or caudex.