Morphology

This plant grows as a shrub 5 decimetres (50 cm) to 17 dm (170 cm) high, with the branches largely leafless and slender. The young twigs are slender, simple, and colored reddish. The lanceolate leaves are 8 to 20 mm long, and 2 to 10 mm wide. The petioles are 1 to 5 mm long.^[3]

The inflorescence is composed of terminal and usually elongate racemes. There are 4 sepals and petals, and 8 stamens. The pedicels are about 4 to 5 mm long, and thicken in fruit. The floral tube is scarlet, and about 2 cm long, widening upwards near the middle. The sepals are colored scarlet, reflexed, and 8 to 9 mm long. The petals are free, erect, and shaped oblong to obovate, around 6 to 9 mm long. The episepalous (growing on the sepals) stamens are slightly exerted outside the mouth, while the epipetalous (growing on the petals) stamens are within the tube. The style is slender and colored red, slightly exerted. The fruit capsule is around 8 to 12 mm long.^[3]

Subspecies

• Xylonagra arborea subsp. arborea – Glandular spreading hairs present on the sepals and young herbage, along with smaller flowers and leaves. Endemic to Cedros Island.^[3][4]
• Xylonagra arborea subsp. wigginsii Munz – The hairs on the younger parts and flowers are very short, and the hairs are not glandular. The leaf blades are up to 20 mm long and 10 mm broad. The floral tube is 2 to 3 cm long. The sepals are 8 to 13 mm long, and the petals are 10 to 18 mm long.^[3][2]