Piper nigrum

Piper nigrum (2n=52,78,104...) commonly known as black pepper is cultivated for its fruit, which is used as a spice and seasoning in the dried form. It is also used in traditional medicine.

Piper nigrum spike on the vine.

Scientific classification

Kingdom: Plantae

Subkingdom: Tracheobionta

Superphylum: Spermatophyta

Phylum: Magnoliophyta

Class: Magnoliopsida

Order: Piperales

Family: Piperaceae

Genus: Piper

Species: P. nigrum

Inflorescence

The inflorescence is a pendulous spike or catkin that emerges from the stem node opposite to the leaves. 

Anthesis

Foliage, Flowers and Fruit of the Pepper Plant.

Anthesis occurs in the evening. The flowers open from the base of spike to the tip (acropetal). Pepper is protogynous, i.e., the gynoecium develops before androecium. So generally flowers lower on the spike are pollinated by pollen dehising from those situated above. So the pollination is by geitonogamy (by means of gravity).

Floral Morphology

Wild pepper is dioecious but cultivated varieties are bisexual, and thus more productive. Whitish to yellow-green small sessile flowers are arranged spirally along the spike. Flowers are bracteolate, with four peltate bracts.

Perianth: The flowers are apetalous, infact lack the entire perianth.

Androecium: The androecium is composed of 2-4 stamens on either side of the ovary. The short filaments bear oval shaped anthers with two pollen sacs.

Gynoecium: Gynoecium is composed of a single (or 3-5) carpel(s). At the center of the flower is the  unilocular superior ovary. The style is short with white star shaped stigma. The stigma is covered with a viscous liquid that favour fertilization.

Fruit

Fruits are round, berry-like, up to 6 mm in diameter, green at first but turning red as they ripen, each containing a single seed. The fruit is botanically a drupe and when dried is called peppercorn. 

Green drupes on spike and white (dried ripe) & black (dried unripe) peppercorns

Arbitrary Numbers
The spikes are usually 7-35cm long and bear 70-100 flowers. 50–60 fruits are borne on each spike. Anthesis lasts about 7-8 days.

Useful Links: 

1. Floral diagram and formula of family Piperaceae
2. Kew Botanical Garden Record