Spathe coloration is generally taxonomically significant though variable depending on the age of the plant. Coloration before anthesis is frequently green on the outside of the spathe but coloration often develops well in advance of anthesis. Commonly coloration of the spathe tube and blade differs with the spathe tube more commonly various shades of green and the spathe blade more commonly white, whitish or whitish-green if the spathe is not green throughout. Even when the spathe is green throughout the spathe blade is typically of a paler shade of green than is the tube. The tube portion of the spathe is commonly colored or tinged with red, maroon or purplish-violet (sometimes with other shades of red, orange or purple) on one or both surfaces. The presence of strong color contrasts (other than merely green and white), so common in Philodendron, is absent in other genera which are deemed related to Philodendron, namely Furtadoa, Homalomena and Anubias (based on the Philodendron Alliance of Mayo, Bogner & Boyce, 1995) or also Cercestis and Culcasia (included in the Philodendron Alliance of Grayum, 1990). This would also be true of other presumed relatives including Dieffenbachia, Montrichardia, Nephthytis, Peltandra, Typhonodorum and even Zantedeschia where there are rarely contrasting spathe colors.

Generally if the spathe is colored on the outer surface it is also colored on the inner surface. Generally the inner surface is much more intensely colored than the outer surface. The coloration of the inner surface of the spathe, though commonly more or less restricted to the spathe tube, may extend well onto the spathe blade, sometimes even to very near the apex, such as in P. breedlovei, P. davidsonii, and P. mexicanum. In some cases, such as P. findens and P. schottianum, the color is merely weakly diffused onto the spathe. At other times only the very base of the spathe is colored, such as P. ligulatum and P. hederaceum. The spathe blade is commonly more extensively colored on the outer surface than on the inner surface. Coloration is highly variable (see below) not only interspecifically but also intraspecifically. Nevertheless most species have spathe blades colored some shade of green or white on the outer surface, often tinged with red, pink, purple or yellow. A few species, such as P. sagittifolium and P. ferruginium (Fig. 167) have purplish spots or blotches throughout much of the exterior of the spathe surface. Although the external coloration of the spathe is usually restricted to the tube portion, the coloration often extends onto the blade, a situation which happens more frequently on the outer surface of the spathe than on the inner surface. Species which have coloration extending well above the spathe tube are P. antonioanum, P. breedlovei, P. dolichophyllum, P. subincisum and P. roseospathum. Sometimes the coloration of the spathe tube may be restricted to the tube, but only near the margins of the open edge such as in P. grayumii and P. malesevichiae. Some species, such as P. dodsonii and P. strictum, have a clearly marked distinction between the color of the spathe tube and spathe blade but at the same time have weak coloration on the spathe blade.

While some species, e.g., P. alticola, P. heleniae, and P. findens show little or no distinction in the coloration of the spathe tube and spathe blade, some species, such as P. dodsonii, P. gigas, and P. fragrantissimum, have distinctly different colors on the spathe blade and spathe tube.

In some cases, e.g., P. antonioanum, P. coclense, P. cretosum, P. edenudatum, P. findens, P. grandipes, P. lazorii, P. ligulatum, P. llanoense, and P. roseospathum, the transition from one color to the next is very gradual. In other cases, such as P. hebetatum, P. immixtum, P. jodavisianum, P. panamense, P. pterotum, P. strictum, P. radiatum, P. rothschuhianum, P. scalarinerve, P. smithii, P. tenue, P. wendlandii, and P. zhuanum, the transition is less gradual but by no means abrupt. Still other species, e.g., P. coclense, P. dodsonii, and P. fragrantissimum show a distinct and abrupt transition in the spathe tube and blade colors.

The list below details those colors or variations in colors represented on the outer spathe blade surface for Central American P. subg. Philodendron. With the exception of those described as being green (7), white (5), greenish white (3), pale green (3) or pale green to greenish white (3) on the outer spathe blade surface, all other colors or color combinations had only one or two representatives. A total of 37 species have outer spathe coloration white or cream at least part of the time. Only 9 species have the outer surface of the spathe blade distinctly colored or heavily tinged with some hue of red or purple.

pinkish white

greenish white

greenish white, sometimes heavily tinged red

greenish to whitish

green to whitish

greenish white to white

white

white, yellow-green medially outside

white tinged reddish

white or cream

white or cream, sometimes red-spotted

creamy white to yellowish green

cream

white to pale green

whitish to pale green or creamy yellow

white to greenish, rarely reddish

dark green

green

pale green

pale green to yellowish green

green to pale yellow-green

green to greenish white

green to white, tinged marroon or red

green to greenish white to creamy yellow

green tinged maroon

green tinged maroon or reddish

green tinged red or reddish-violet

green or red

green to purplish

dark green or with purplish tinge

yellow-green

yellow-green, tinged reddish dorsally

yellowish green

green to yellowish green, creamy white or lemon yellow

pale green to white

pale green to white or green, tinged pinkish red

medium green, whitish or reddish green

medium green to dark green outside

pale green to whitish, tinged violet-purple

pale green to white, tinged pink

pale green to greenish white to yellowish green

medium to pale green

medium green

medium green, pale yellow to whitish at apex

pale green, yellowish at margins

pale greenish

pale green or white, tinged red near base

pale green to greenish white

pale green to greenish white to yellow-green

green tinged white

green to greenish white to creamy yellow, tinged with violet

pale greenish white to white

light green

light green to creamy yellow to white

light green to whitish, tinged purple

greenish yellow

creamy yellow

pinkish red, tinged green

red

maroon, paler toward apex

The inner surface of the blade is usually paler in color than the outer surface, frequently pale green or white but sometimes tinged in part with yellow, red, pink, maroon or violet-purple. Usually the latter coloration is more intense toward the base and the coloration usually merges imperceptibly with the coloration of the spathe tube. A total of 53 species have at least sometimes have the interior spathe coloration either pale green, greenish white, white, or cream. A total of 29 taxa have the inner spathe coloration at least sometimes tinged or solid pinkish, red, or some variation of red or purple. The list below details the various colors and combinations of colors for the interior of the spathe blade for Central American P. subg. Philodendron.

creamy

creamy white

white

white to pale green

white to pinkish

white tinged red near base

white tinged maroon

white to greenish

whitish

whitish to creamy yellow

whitish green

whitish, suffused maroon midway

greenish white

greenish to white

pale greenish white

pale greenish cream

very pale green to white

pale green

pale green to white

pale green to whitish and suffused red

pale green to creamy white to white

pale green, cream, whitish or suffused with red

pale green to greenish yellow

pale green to maroon

pale green, tinged red near base

medium green tinged pinkish, red toward apex

medium green tinged reddish to maroon

greenish white tinged violet-purple

greenish white to creamy-white, tinged red-purple in throat,

to pale yellow green or white

green to whitish

green to whitish, suffused with red

pale yellow-green

red

reddish

pinkish

pinkish red to white, pale greenish white or pale green

red to white

red to maroon or greenish white

pale maroon to white

dark maroon to cream

purplish, whitish near margin

The list below details those colors or variations in colors represented on the outer spathe tube surface for Central American P. subg. Philodendron. A total of 59 species lack color other than green or white at least sometimes. A total of 26 species have spathe tubes which are at least sometimes predominantly solidly colored or so heavily tinged as to appear colored. All but three of these are predominantly green, not white. The outer spathe tube surface is only slightly less variable in color than the inner spathe surface but many more species lack color on the outer surface than on the inner spathe surface. With the exception of those described as being solid dark green (6), medium green (21) on the outer spathe tube surface, all other colors or color combinations had fewer than three representatives.

dark green

dark green or dark purple-violet

dark green or purple to violet-purple to red or pinkish

green to purple-violet

green tinged purple

green spotted violet-purple

green tinged violet-purple at base

green tinged red-purple to red

green tinged red

greenish, sometimes reddish tinged greenish, tinged red

dark green to medium green

medium green

medium green, sometimes tinged reddish

medium green to greenish white

medium green to olive-green

pale to medium green

pale to medium green, sometimes tinged red

pale green

pale green to yellowish green

pale green, pale violet-purple near base

light green, sometimes tinged maroon at base

white

white to greenish white

white tinged red or purple

dark maroon

maroon

maroon or reddish

purple or maroon

reddish maroon to reddish purple to green

dark violet-purple

purplish violet

purple

red-maroon

red-purple to dark reddish to green

reddish green, medium green or dull purple-violet

reddish or dark maroon

reddish to purplish to dark purple

magenta

The list below details those colors or variations in colors represented on the inner spathe tube surface for Central American P. subg. Philodendron. Of the 91 species for which spathe tube color is known, 29 species are described as having inner spathe tubes that are at least sometimes uncolored within, either green or white (though sometimes tinged with color at base). The remainder are colored with variations of red or red-purple. With the exception of those described as being dark maroon (5 species), dark violet-purple (5 species), or red (4 species) on the inner spathe tube surface, all other have colors or color combinations with even fewer representatives.

green

pale green

pale green to greenish white to white or pinkish red

pale to medium green

pale yellowish green

green to white

greenish to whitish

greenish white

greenish white to creamy white

pale green, tinged violet-purple at base

pale green to white

pale green to maroon

greenish white, green or sometimes red or violet-purple

green to dark violet-purple

bright red-violet

bright red-violet to dark maroon

cherry-red

dark maroon

dark maroon to dark purple, red-violet or violet

dark maroon to violet-purple

dark maroon, suffused onto base of blade

dark red-violet

dark reddish violet

dark red to red-purple

dark violet-purple

deep magenta

deep maroon, red or crimson

maroon

maroon to crimson, pale red-violet or dark purple

maroon to red

maroon, dark red, crimson or purple

maroon, suffuse onto blade

maroon-red

light red to maroon

red

red-violet

purple-violet

purple-violet to light maroon

purplish violet or crimson

purple

purple to reddish

red, pink or purple

red-purple to dark reddish

reddish to dark maroon

reddish to maroon

reddish to pale violet-purple

reddish violet to maroon to magenta

red or pale reddish

red or violet-purple

red or maroon at base

red to maroon or dark violet-purple

red to red-violet or purplish

red to reddish purple

violet-purple to red

white

whitish

whitish, violet-purple near base

white, tinged red or purple

white to pale green, sometimes red at base

The ecological significance of the frequently darker colors on the inside of the spathe tube in contrast to the paler colors of the spathe blade is uncertain. It seems unlikely that either the contrasting colors or the dark color of the spathe tube act in attracting pollinators. The presumed pollinators, dynastine scarab beetles, (see section on Pollination Biology) are believed to orient more by smell than sight (Faegri & van der Pijl, 1979; Gottsberger & Silberbauer-Gottsberger, 1991). Moreover, their normal arrival time under near dark conditions would probably preclude their seeing contrasting colors in any event. Moreover, the dark coloration is usually restricted to the spathe tube, often not even visible in good light when near the mouth of an open spathe. It is more likely that the dark colored spathe tube acts to darken the environment of spathe tube, encouraging these crepuscular beetles to enter there and stay for an extended period of time. Mayo (1986) pointed out that since neither P. subg. Pteromischum nor P. sect. Meconostigma have color contrasts in the spathe blade and tube, that P. subg. Philodendron may have different pollinators. Although not enough pollinators are yet been identified to confirm this possibility, there seems to be little evidence that the pollinators will prove to be distinct (see section on "Pollination Biology". Certainly some beetle species, such as Erioscelis proba Sharp, are known to visit species of both P. subg. Philodendron and P. subg. Pteromischum (Grayum, 1996). See also "List of Pollinators" below.

Extrafloral nectaries on both the exterior of the spathe and on the peduncle secrete large droplets of a viscous, somewhat sweetened substance. Mayo (1986) has shown that these may consist of a cluster of stomata and pointed out their ecological significance as extrafloral nectaries.

Apparently unique to Philodendron is the secretion of resin on the inner surface of the spathe. No other genus of Araceae is known to exhibit this feature (Mayo, 1991). Mayo (1986) enumerated four different types of resin canals at least two of which occur among Central American Philodendron. One type, represented by P. tripartitum, has large diameter resin canals imbedded just beneath the epidermis on the inner surface of the spathe. Resin is secreted directly onto the surface. Another type, represented by P. smithii, lacks resin canals on the spathe but instead has resin canals in the staminate zone of the spadix

The two other types of resin canals pertain to P. subg. Meconostigma and P. subg. Pteromischum respectively. In the former, characterized by P. bipinnatifidum (Schott) Schott, the resin canals are "J" shaped, and tangential, arising in the aerenchyma and extending to the surface. In the latter, characterized by P. sonderianum Schott, the resin canals are evenly distributed between the aerenchymata and epidermis and are parallel to the surface rather than arising in a J-shaped fashion.

Resin canals usually are present in the lower 1/2 to 2/3 of the spathe blade and sometimes also the upper portion of the spathe tube. For members of P. subg. Philodendron the resin canals are generally colored reddish, red-purple or orange to brownish and generally somewhat intermittent, as in P. sulcicaule, though sometimes continuous, as in P. immixtum, P. mexicanum, P. sagittifolium, and P. wilburii. They are always oriented vertically, paralleling the veins of the spathe. The resin canals actively secrete a resinous liquid at anthesis which wells up onto the surface of the spathe and sometimes runs down the spathe below the resin ducts. The resin is generally very sticky and probably functions in causing pollen, sometimes itself not particularly sticky, to adhere to the bodies of the beetle pollinators as they leave the spathe.