Who were involved in genesis of Baltic amber?

Sciadopitys verticillata, were involved in the genesis of Baltic amber.

Conifers of the family Sciadopityaceae, are closely allied to the sole extant representatives.

Sciadopitys verticillata is commonly known as Japanese Umbrella pine, or as コウヤマキ (koya-maki) in the Japanese language.

The English name ‘Umbrella pine’ refers to the whorls of leaves resembling the spokes of an umbrella; the Latin Sciadopitys is a translation of this.

Sources:

http://conifersociety.org/conifers/conifer/sciadopitys/verticillata/

 and 

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2817186/