Table 2 Dichotomous key to seven species in Alpinia , Amomum, and Elettaria genera based on anatomical characteristics of seeds

1. Fruit a capsule, axile placentation, seeds with arils and numerous seeds attached to the central axis of an ovary with three locules

2a. Hypodermis of testa comprising one layer of cells with pigment

3a. Inner side of oil cell layer with several layers of pigmented cells

4a. Pigmented cell wall not distinct

5a. Ratio of thickness of lumina to endotesta palisade sclerenchymatous

cells 1:5–1:4

1. Amomum kravanh

5b. Ratio of thickness of lumina to endotesta palisade sclerenchymatous

cells 1:10–1:20

2. Amomum subulatum

4b. Pigmented cell wall distinct and shrunken

3. Amomum tsao-ko

3b. Inner side of oil cell layer with one layer of obliterated cells

4. Elettaria cardamomum

2b. Hypodermis of testa comprising one or more layers of cells without pigment, several layers of pigment cells scattered with oil cells

6a. Ratio of thickness of lumina to endotesta palisade sclerenchymatous

cells approx. 1:2

7a. Oil cells in 1–3 layers

5. Alpinia katsumadai

7b. Oil cells in 1–2 layers

6. Alpinia zerumbet

6b. Ratio of thickness of lumina to endotesta palisade sclerenchymatous

cells 1:5–1:4

7. Alpinia galanga