Abnormal flowers in genus Alpinia

There are six types of abnormal flowers in Alpinia described in this paper, namely 2-stamens, 1.5-stamen, 1-stamen, stamen with only one theca, stamen absent and twin-flower. A different morphological nature of subulate appendage is proposed: it might be the androecial appendage, i.e. appendage of stamen or labellum, but not of staminode. The second type of the abnormal flowers with 1.5-stamen is regarded as synapomorphy, which is absent in the extant taxa, of the four ginger families, from which were derived the Zingiberaceae and Costaceae with one functional stamen or the Marantaceae and Cannaceae with half stamen. The diversification of the number of stamen in abnormal flowers might be a recurrence of the evolutionary history of stamen in ginger families.