The cataphyll is an important part of a lot of plants. In aroids it can help alert you to a new leaf that is emerging. A cataphyll is a modified leaf that surrounds a new developing leaf and protects it as it emerges. In some cases, the morphology and characteristics of the cataphyll can help determine the differences between species.
Some cataphylls are easy to see like the one on this Alocasia cuprea
But not all species of Alocasia make cataphylls like that one. Some just have the cataphyll as an extension of the existing petiole of the last leaf to emerge, like in this A. macrorhizza albo-variegata
Some cataphylls die off after the leaf emerges like this old brown one on this Philodendron spectabile. This should not be mistaken for a problem with the plant
Others do not die off but instead become ornamental themselves, as on this Philodendron grazielae
Creeping terrestrial aroids like Philodendron gloriosum whose leaves arise from the buried trunks do not show cataphylls
Some large growing root climbers like this Rhaphidophora decursiva incorporate a terminal cataphyll as the plant climbs
And some are just plain gorgeous....like the ones on this Philodendron 'Ace of Spades'. If you look really close you can see the new red leaf about to emerge
