In the taxonomy of Philodendron probably no morphological feature is more diagnostic than is the cataphyll (sylleptic prophyll of Ray, 1987a). It is the single feature that makes the preparation of keys to species of Philodendron easier than those for Anthurium. In P. subg. Philodendron 56 taxa have cataphylls which are deciduous while there are 48 taxa which have persistent cataphylls. Of these six persist intact, 25 semi-intact and 17 as fibers. While a few species have cataphylls which are slow to become deciduous and others which have persistent cataphylls that eventually fall off, relatively few species are difficult to place in one or the other category. Cataphylls persist within the sections as follows:

Philodendron exhibits considerable variation and remarkable consistency in cataphyll characters. Among the most valuable characters is whether the cataphylls are deciduous or persistent. Generally speaking cataphylls are deciduous in vines and persistent on appressed-climbing plants but there are exceptions in both groups. Cataphylls are bract-like modified leaves which function in the protection of newly emerging leaves. For vines the cataphyll becomes functionless once the leaf has emerged and they generally are promptly deciduous. Typically they recurl away from the stem on vines and eventually become loosened from the base and fall free such as on P. purpureoviride (Fig. 320) Alternatively, on epiphytes or appressed-climbing hemiepiphytes with short internodes the cataphylls can not easily fall free (Fig. 15; Fig. 115; Fig. 312). Though they may fall free from the stem and invariably promptly dry and usually become withered or weather into fibers, they are often prevented from falling free by the tight cluster of petioles generally found on plants with short internodes. They do regularly fall free on some species with short internodes such as P. warszewiczii (Fig. 443) or P. dressleri (Fig. 160) but typically cataphylls persist on species with short internodes (Fig. 302, P. pirrense; Fig. 358, P. scalarinerve). Persistent cataphylls are often persist in an organized mass around the apex of the stem (Fig. 382, P. squamicaule). They may persist intact such as in P. grandipes (Fig. 204), P. jodavisianum (Fig. 248), P. roseospathum (Fig. 341, 343) or they may have a very thin, flaky epidermis which remains intact in large pieces as in P. dodsonii, P. hebetatum or P. strictum (Fig. 398) but more frequently they decompose at least partially to expose a network of fibers beneath the epidermis (Fig. 258, P. lazorii) and even more frequently the epidermis disappears all together (Fig. 202, P. glanduliferum; Fig. 253, P. jodavisianum; Fig. 370. P. schottianum). Ecologically the mass of cataphyll fibers serves a useful purpose, namely to prevent desiccation of the stem apex and especially the young roots which emerge through the moist cataphyll mass. In some species the layered cluster of cataphylls provides a sodden mass (Fig. 370, P. schottianum); Fig. 63, P. antonioanum; Fig. 99, P. chiriquense) and in some cases the youngest cataphylls are protected by a gelatinous, slimy fluid which fills the interstices of the cataphyll mass. Cataphylls are generally rigid and firm when fresh which protects the young leaf from physical damage. Some are thick and fleshy with considerable amounts of liquid in their tissues. As these begin to decompose they may yield large amounts of watery or even gelatinous sap. This fluid may even be important as a lubricant for the emerging leaf to prevent damage to the tender tissues or to prevent its desiccation on first emerging.

A typical cataphyll is narrowly triangular, 2.3-4 times longer than wide, with the base as broad as the circumference of the stem. Cataphyll length is somewhat proportional to leaf size on any species with the length ranging from (5)10-50(70) cm long and to (1.5)2.5-18(31) cm wide. Since the cataphyll is affixed around the complete circumference and eventually becomes deciduous, it leaves a distinct scar on the stem. These cataphyll scars alternate with the petiolar scars and may be conspicuous (Fig. 10, P. davidsonii var. davidsonii) or inconspicuous (Fig. 9, P. rothschuhianum). Fresh cataphylls are usually green, though in some cases almost white, as in P. wilburii or they may be bright red, or may be heavily tinged red on exposed parts, such as in P. antonioanum, P. niqueanum, and P. tysonii or reddish as in P. glanduliferum, P. grandipes and P. pirrense. Cataphylls are often variously ribbed. In cross-section they are frequently sharply D-shaped in outline but may be completely terete. When terete they may be unribbed or bluntly 1- or 2-ribbed (Fig. 60, P. annulatum; Fig. 16, P. warszewiczii; Fig. 17, P. schottianum) or sometimes sharply 1-ribbed. Those cataphylls which are D-shaped are often bluntly to sharply raised along the edges of the flat side so that they appear bluntly to sharply 2-ribbed, as in P. pseudoauriculatum (Fig. 313). The ribs may be moderately low and closely spaced as in P. panamense (Fig. 298). In some cases the ribs are slender and knife-edged and the ribs themselves may be as much as 1 cm high as in P. auriculatum (Fig. 72) and P. annulatum (Fig. 60). Typically the cataphyll is coriaceous and sometimes very thick and succulent, frequently more than 1 cm thick toward the base on larger species. The cataphylls have a subcuticular fibrous reticulum and when fresh the interstices of the fibers are often filled with water or mucilage. Since epiphytes are often subject to harsh conditions this is probably important to protect the growing point of the plant and the newly emergent leaves from extremes in temperature and humidity. Though the cataphylls soon lose their moisture after they have opened, many persist semi-intact or as an organized network of fibers so they continue to add protection to the stem apex. Even after the cataphylls are reduced to a mass of fibers they still retain moisture much as a pile of straw does after a rain.

Useful taxonomic characteristics are found in the manner in which the cataphylls weather and persist. This mass of cataphyll may be quite distinctive both in the degree to which it persists intact and the degree to which it weathers to fibers. The coloration of the cataphyll fibers is also variable, with colors ranging from almost white to tan, various shades of brown or yellow to reddish or reddish-brown. They are often marked with short lineations in the same manner as are the petioles (Fig. 16) Some species have the network of fibers highly organized while in other species the fibers are very disheveled such as in P. tenue or P. panamense. In most species the epidermis promptly falls off while in some all or parts of the epidermis persist. In P. schottianum the distinctive yellowish epidermis of the cataphylls is one of the most characteristic features.

In time the lowermost cataphylls simply rot away even for species with a large cataphyll mass so that ultimately the oldest part of the stem is visible. By this time the stem is quite old and there are few visible features worth noting.

For many species the entire cataphyll does not persist, but rather only the basal part of the cataphyll. Despite the fact that the stem is not covered with a large cataphyll mass, the stem is not easily visible. In such species the cataphyll bases seem to persist longer than in those cases where the entire cataphyll eventually falls free after persisting for a time.