Vanilla planifolia

Vanilla planifolia (2n=32) is a species of vanilla orchid and is one of the primary sources for vanilla flavouring, due to its high vanillin content. 

Vanilla planifolia inflorescence on the vine

Scientific classification

Kingdom: Plantae

Phylum: Angiosperms

Class: Monocots

Order: Asparagales

Family: Orchidaceae

Subfamily: Vanilloideae

Genus: Vanilla

Species: V. planifolia

Vanilla planifolia 1887 illustration from Köhler's Medicinal Plants

Inflorescence
Inflorescence emerge as a light green protuberance from the leaf axil. It is a 5-8 cm long generally un-branched (rarely branched) raceme. 

Anthesis

Anthesis is in the early morning. Flowers open acropetaly i.e., from the base of the inflorescence upwards. Each inflorescence has only a single flower open at any one time and a flower lasts only one day.

Floral Morphology

Longitudinal section of Vanilla flower showing Pollinia and Rostellum

Vanilla bears large zygomorphic bisexual flowers that are pale geen or cream or yellow in colour. Flowers are pedicellate, borne on a short pedicel and bracteolate, each flower is subtended by a small pointed bract. flower is turned upside down   (resupinate) as it develops so the labellum is on the bottom.

Perianth: 3 narrow pointed oblong sepals constitute the calyx. Corolla consist of 2 upper petals that resemble the sepals but are slightly smaller, and a trumpet shaped labellum or lip.

Androecium:  A single pollinia is attached to labellum, bearing at its tip 2 pollen masses covered by a cap/hood. 

Dried Vanilla pods with seeds inside

Gynoecium: Concave stigma is  situated below the pollinia is separated from it by a thin flap-like membrane or rostellum, which prevents natural pollination.  Style fused with the filaments of the stamen form the column or gynostemium. Ovary is inferior and long. 

Fruit

Fruit a pendulous, narrowly cylindrical capsule, obscurely 3-angled, splitting longitudinally when ripe. Seeds numerous, globose, non-endospermous, black.

Arbitrary Numbers
On a single wine 7-15 inflorescence emerge in a season. Each inflorescence carries 15-25 large flowers. It takes 50-60 days from floral initiation to anthesis. Flowering period extends 14-30 days. 

Useful Link:Floral formula and floral diagram of Orchidaceae family