The Thyrsus *, or Thyrse, is a mode of inflorescence very nearly allied to the panicle, being, in fact, a panicle contracted into an ovate, or egg-shaped form. In the thyrse, the middle footstalks, which are longer, extend horizontally, whilst the upper and lower oes are shorter, and rise up vertically.
Source: wiktionary
The example of the thyrse of Eugenia leads us to understand several inflorescences which resemble also racemes or panicles; such are the thyrses of the Lilac.
Source: wiktionary
1998, D. W. Stevenson, M. Colella, B. Boom, Rapateaceae, Klaus Kubitzki, H. Huber (editors), The Families and Genera of Vascular Plants, Volume IV: Flowering Plants, Monocotyledons: Alismatanae and Commelinanae (except Gramineae), page 417,
The number of spikelets is variable, and some genera have thyrses with 70 spikelets (Saxofridericia, Spathanthus) or only 1-3 spikelets per inflorescence (Stegolepsis, Monotrema).
Source: wiktionary