Ecology and Life Forms of Araceae

49 Pages·2009·1.81 MB·English

4 AROIDEANA, Vol. 11, No.3
Ecology and Life Forms of Araceae
Thomas B. Croat
Missouri Botanical Garden
RO.Box299
st.
Louis, Missouri 63166-0299
INTRODUCTION casts a darker shadow) where a physio
Araceae, a family of herbaceous mono logical change takes place allowing them
cotyledons with 106 genera, is a com to grow toward light (Strong & Ray,
plex group in terms of life form and 1975). They grow as appressed epi
ecology. The family is widespread, with phytes on trees or as vines in the canopy.
almost an equal number of genera in Others begin their lives as true epi
both the Old and New Worlds, but with phytes, some reconverting to hemiepi
the majority of species occurring in the phytes by producing long, dangling roots
New World tropics. A few genera range contacting the forest floor below.
into north temperate regions with one
Some species, especially members of
species ranging to at least 63 degrees
subfamily Monsteroideae, have heterob
north latitude. Few aroids range into
lastic development with leaf and stem
temperate regions of the southern hemi
morphology reflecting the differences in
sphere; the most southernly being Pistia
their growth phases. Juvenile plants may
stratiotes L., which can be found through
produce a small terrestrial rosette of
36 degrees south latitude in Argentina.
leaves, then grow rapidly, producing a
The family occupies a wide variety of life
few small leaves on long internodes. The
zones and habitats throughout its range,
preadult leaves of the first hemiepiphytic
extending from tropical dry to pluvial
phase of such plants are often very
rainforest, but also ranges into subarctic
marshes, tropical swamps, cloud forests, distinct from the adult leaves. Many such
cold windswept montane plains and species are able to convert again and
semi-arid to arid coastal plains. The again from adult growth (consisting of
family has many species which will not short, thick internodes) back to juvenile
tolerate any degree of frost or cold such growth (with elongate internodes bear
as Anthurium brownei Masters, as well ing smaller leaves), either to establish
as some, like Symplocarpus foetidus (L.) more adult plants with a rosette of leaves
Nutt., which actually emerge from snow or to survive the dynamics of an ever
covered ground. changing forest, complete with treefalls
The most interesting aspect of the and falling branches (Ray, 1987). Other
family's ecology is the diversity of adap hemiepiphytic species are vines which
tive life forms. These range from sub branch and produce growth throughout
merged to free-floating, and emergent the lower and middle levels of the
aquatics to terrestrial plants and to canopy. These species (e.g., Philoden
epilithic or epiphytic forms which may dron scandens K Koch & Sellow) ac
be true epiphytes or hemiepiphytic complish long-term survival by having a
(growing on trees but rooted in soil). portion of their biomass in a part of the
Hemiepiphytism is diverse itself, with canopy which survives any particular
some species beginning their lives as treefall (Pefialosa, 1975). Even true epi
terrestrial seedlings, then growing phytes rarely succumb promptly to a fall
skototropically (toward darkness) until from their host tree, but instead con
they arrive at the nearest suitable tree tinue to flower and fruit on the ground
( usually a relatively large one which for a limited time.
T. Croat, 1988 5
DISCUSSION by only one genus, with one pantropic
The following is an outline and discus and variable species. Pistia stratiotes L.
sion of life form diversity in the Araceae has a short stem and a rosette of
(see Appendix III for a glossary of aerenchymatous, buoyant leaves, with a
terms): cluster of fine, hair-like roots below. It
1. Aquatic plants occurs mainly at lower elevations and
1.1 Submerged aquatics inhabits mostly open, fresh waters at the
1.2 Free-floating aquatics edges of slow-moving streams, lakes and
1.3 Emergent aquatics ponds. This species is remarkably suc
2. Terrestrial plants cessful in using mostly vegetative repro
3. Epilithic plants duction, often totally clogging small to
4. Epiphytic plants large waterways in a short period of
4.1 Hemiepiphytes time.
Vines
1.3 Emergent Aquatics
Appressed climbers
Emergent aquatiCS make up a very
4.2 Epiphytes
large group within Araceae. Many genera
1.1 Submerged Aquatics have at least some species which spend
Jasarum steyermarkii Bunting has per all or part of their lives rooted in
manently submerged leaves and is the standing or moving water. Temperate
only true example of this life form North America is particularly rich in
among neotropical Araceae. It grows aquatiC or semiaquatic genera. Most,
rooted in moving streams on the escarp including Acorus, Calla, Lysichiton,
ment of the Guayana Highland where it Orontium, Peltandra and Symplocar
is endemic (Bogner, 1985). When it pus, grow in swampy or marshy areas,
flowers, the scape is protruded above lakes, ponds, or along the edges of
the level of the water. Many rheophytes, creeks. Arisaema triphyllum (L.) Torr.
however, may spend a portion of their is also reported as sometimes occurring
lives underwater with no apparent harm, in swampy areas (Small, 1933; Correll &
but flowering occurs when the plants are Correll, 1972).
mostly emerged and have only their Some emergent aquatics, e.g., Mon
short stems below water. Species of trichardia arborescens (L.) Schott, Pel
Acorus, Anubias, Lagenandra, Spa tandra virginica (L.) Kunth, Cryptoco
thiphyllum and especially Cryptocoryne ryne ciliata (Roxb.) Fischer ex. Schott
are used as aquarium plants and may be (D. Nicolson, pers. comm.) and Typhon
submerged completely for indefinite pe odorum lindleyanum Schott O. Bogner,
riods of time without apparent injury. pers. comm.), occur in tidal zones.
Even Dieffenbachia has been used in While most emergent aquatiC genera
aquaria (D. Nicolson, pers. comm.) in the neotropics are well-rooted, terres
The Asian tropics, in contrast to the trial plants, some are epilithic, such as a
American tropics, have large numbers of rheophytic group of Anthurium (A.
submerged aquatics, the most important andicola Liebm., A. sytsmae Croat, A.
being the genus Cryptocoryne. Members rupicola Croat and A. antioquiense
of this genus spend most of their lives in Engl.) and SpathiphyUum (S. quin
shallow water, but typically flower at diuense Engl.), although the percentage
periods of low water (when their leaves of rheophytic species for each genus is
have emerged above water level) or low.
when the water level is low Oacobson, The Asian tropics, on the other hand,
1980, 1982;). Bogner, pers. comm.). are much richer in rheophytic plants.
Aridarum, Bucephalandra, Cryptoco
1.2 Free-floating Aquatics ryne, Furtadoa, Heteroaridarum, Hotta
Free-floating aquatics are represented rum, Lagenandra, Phymatarum, Pipto-
6 AROIDEANA, Vol. 11, No.3
spatha, some Homalomena and some considered aquatiC in the true sense.
Schismatoglottis, have the majority, or Many are, in fact, principally epiphytic
all, of their species occurring along or in genera which find steep, well-drained
streams, frequently clinging to rocks on stream banks good substitutes for the
stream banks (van Steenis, 1981). normal epiphytic habit (see below).
The majority of emergent aquatic
2. Terrestrial Plants
plants are not rheophytic, but rather
occur in flowing or standing water. The terrestrial habit is predominant
Among the New World genera, which for aroids on a world-wide basis. Terres
are nearly always found growing in trial genera are the most diverse ecologi
water, are Dracontioides, Montrichar cally, occurring in humid to very dry
dia and Urospatha. Other genera, such as habitats, in secluded forest understory
Diejjenbachia, Philodendron and Spa and in open, exposed areas. While most
thiphyllum have some species growing genera comprise mainly understory
in aquatic or marshy situations. An plants in primary forest, some range into
aphyllopsis (A. Hay, 1989) grows along savannas, exposed steppes, alpine mead
streams or in swampy areas in the ows and even into semidesert areas.
understory and survives partly underwa Terrestrial aroids range in habit from
ter part of the year. Homalomena some caulescent plants (Diejjenbachia and
times occurs in varzea forest in the Aglaonema) to tuberous plants (Amor
Amazon basin, and survives underwater phophallus, Arum and Dracontium), to
conditions for long periods, then toler rhizomatous (rarely also reported as
ates swampy situations until the water cormose - see Colocasia, Therio
fully recedes. phonum or 1jIphonium in Appendix II.)
In addition to the rheophytic genera and to subscandent plants ( Cercestis and
mentioned above, there are a number of Culcasia).
other, chiefly emergent aquatics in Asia A large percentage of terrestrial aroids
usually growing along streams or in have rhizomes, or short stems with short
swamps. They differ in that they are not internodes, which usually creep over the
usually clinging to rocks or to steep surface of the soil or just beneath the soil
banks, but are rooted along the edges of surface. Rhizomes may be deeply rooted,
water courses and usually have subterra as in Cyrtosperma and Spathiphyllum,
nean root systems. These include most but most are weakly or loosely rooted. A
species of Cryptocoryne, Cyrtosperma, few species of Anthurium (e.g., A.
as well as Anubias, Aglaodorum (in ochranthum K Koch, A. pluricostatum
brackish water), Lagenandra, Lasia and Croat & Baker) and Philodendron (e.g.,
Podolasia. P. grandipes K Krause) are deeply
Africa, a generally much drier conti rooted terrestrial plants, although these
nent than Asia or America, has relatively genera are typically epiphytic.
fewer exclusively aquatiC genera, al Most of the rhizomatous creeping
though Anubias has species which are genera, as well as caulescent plants like
principally aquatic. Lasimorpha sene Dieffenbachia and Aglaonema, have the
galensis Schott from tropical West Africa apical portion of their stems erect with
is also an emergent aquatic. In Madagas the older part reclining. Typically, when
car (also introduced in surrounding a plant reaches a certain height, the
islands), 1jIphonodorum is almost al weight of the added growth causes the
ways found in standing water. lower part of the stem to recline. As a
Many other genera, in both the Old result, older plants of Diejjenbachia,
and New Worlds, frequently grow on Xanthosoma and terrestrial Rhodospa
stream banks but rarely come in direct tha may have stems extending for more
contact with the water and cannot be than a meter over the forest floor.
T. Croat, 1988 7
Paleot ropical terrestrial aroids are identical to the conditions an epiphyte
often direct ecological and growth form encounters while growing on tree
counterparts of neotropical genera with trunks. The distinction between an epi
out necessarily being phylogenetically phyte and an epilithic plant is often
related. For example, Amorphophallus blurred as well (see below).
(Aroideae) and Anchomanes (Philoden In the neotropics, there is a total of 22
droideae) of the paleot ropics look super strictly terrestrial genera with 267 ter
ficially like Dracontium (Lasioideae) of restrial species (including emergent
the neotropics and behave in the same
aquatics), with perhaps an additional
manner, Le., an inflorescence being pro 250 species in the genera Anthurium,
duced before the single large leaf is Philodendron and Rhodospatha (genera
produced. which are largely epiphytic). The major
Among the temperate North Ameri ity are inhabitants of the humid, warm,
can genera, all except Arisaema, are tropical areas, which contribute 14 gen
associated with the aquatic habitat, era and almost 500 species. Ten addi
though most, including Acorus, Calla, tional genera with 25 species occur
Lysichiton, Peltandra and Symplocar principally in cooler or drier habitats in
pus may sometimes be found on dry land mostly subtropical or temperate South
but rarely far from water. Orontium is America, while temperate North Amer
always aquatic. Even some species of ica contributes an additional six genera
Arisaema (A. dracontium (L.) Schott) and 13 species (see Appendix I for the
are most frequent in swamp forest and estimated number of terrestrial species
riparian habitats (M. Grayum, pers. in each group).
comm.).
Many of the genera, especially in the
Most neotropical terrestrial species southern part of the neotropics, are
are understory plants occurring in better adapted to growing in harsher
humid to wet primary forest, at the edges conditions. Because of the latitudes or
of primary forests or in open areas in elevations at which they occur, they are
forests, or along stream banks. The adapted to relatively extreme conditions
genera involved are Anaphyllopsis, Ca of drought or cold. These genera include
ladium, Chlorospatha, DiejJenbachia, Asterostigma, Gorgonidium, Mango
Dracontium, Pilarum, Spathiphyllum, nia, Scaphispatha, Spathantheum, Spa
Ulearum, Xanthosoma and Zomicarpa thicarpa, Synandrospadix and Tac
as well as some species of Anthurium, carum, as well as some species of
Philodendron, Rhodospatha and Steno Xanthosoma. All are tuberous, and most
spermation. The habit of Zomicarpella have an interrupted growth period due
is also that of an understory herb. A few to conditions of cold (as is the case of
other genera, including Stenosperma those in Argentina or at high elevations
tion, may occur on steep banks, where in the Andes) or to drought, when leaves
drainage is good and the ecological are deciduous. While some genera usu
situation closely matches the epiphytic ally occur as understory plants, (Asteros
habit, but this is commonly true only in tigma, Spathantheum, Spathicarpa and
areas of disturbance, such as along some species of Taccarum), other gen
eroding river banks and roadcuts. era frequently occur in more open
At higher elevations on steep slopes, habitat (Mangonia, Gorgonidium,
and especially in cloud forests, the Scaphispatha, Synandrospadix and
distinction between the epiphytic and some species of Taccarum and Xantho
soma).
terrestrial habit may break down alto
gether. The general accumulation of A higher percentage of paleotropical,
debris on the forest floor and good as opposed to neotropical, genera are
drainage makes such situations virtually terrestrial and are more ecologically
8 AROIDEANA, Vol. 11, No.3
diverse. Most of the endemic African Australia has seven indigenous terres
genera are terrestrial in habit. On main trial genera, each with only one or two
land Africa these include Ancbomanes, species. These are Alocasia, Amor
Anubias, Callopsis, Gonatopus, Nepb PboPballus, Colocasia, Gymnostacbys,
tbytis, Pseudobydrosme, Stylocbaeton, Remusatia (also epiphytic), Sauroma
Zamioculcas and Zantedescbia, as well tum and Typbonium. Only Gym
as some species of Cercestis and Culca nostacbys is endemic at the generic level
sia. In the Malagasy area, terrestrial (Amorpbopballus, Alocasia and 1Y
genera include Aropbyton, Carlepbyton, Pbonium have endemic species). Aside
Colletogyne and Prota rum (Seychelles). from the terrestrial species, there is one
As in the neotropics, most of the species aquatic (Pistia), one epiphytic (Re
in these genera occur in the understory musatia vivipara (Roxb.) Schott) and
of primary, mostly humid forests. In six hemiepiphytic species, so that sixty
deed, with the exception of a few species percent of the araceous flora is terres
of two genera, Potbos and Rbapbido trial.
pbora, most of which occur in Asia, all of
Ecologically, the Asian terrestrial spe
the African genera are basically terres
cies are more complex than those in
trial. The genus Anubias has some spe
Africa. As is the case in the American
cies which are aquatic at least part of the
tropics, the majority of the terrestrial
time, and both Cercestis and Culcasia
species are understory plants occurring
have species which are hemiepiphytic.
in humid primary forests, but a higher
A high percentage of the endemic percentage of Asian genera occur in
African genera are adapted to a dry marshy areas. The greatest concentra
season and have developed tuberous tion of genera is in the Malesian region,
stems or rhizomes. These include An mostly in evergreen forests, but large
cbomanes, Aropbyton, Carlepbyton, numbers of species also occur in mon
Colletogyne, Gonatopus, Protarum and soon forests further to the north, with a
Remusatia. In addition, all of the north respectable number of species ranging as
African genera of Mediterranean climate far north as China and Japan. Asian
areas (see below) are tuberous, as are understory genera include Aglaonema,
the three genera which also occur in Alocasia, Amorpbopballus, An
Asia, namely Amorpbopballus, Sauro apbyllum, Arisaema, Colocasia, Crypto
matum and 1Ypbonium (the last natural coryne (usually in dried out pools and
ized in Africa). Stylocbaeton, though not also included under "rooted aquatics"),
tuberous, accomplishes the same ability Cyrtosperma, Hapaline (usually terres
to survive long periods of drought by trial, rarely epiphytic), Holocblamys,
having a short rootstock with thick Homalomena, Remusatia (also in
succulent underground roots. cluded among "hemiepiphytes"),
Sauromatum, Scbismatoglottis, Spatb
Not surprisingly, all species occurring
ipbyllum, Steudnera and 1Ypbonium.
in Europe and in the Mediterranean
Pycnospatba is also an understory herb.
region are terrestrial and most (except
Arisarum, Calla and the introduced The majority of the terrestrial Asian
Acorus, which are rhizomatous) are genera have rhizomatous stems, though
always tuberous. Most species of Arum some (Amorpbopballus and Pycnospa
are adapted to dormancy during the tba) have tuberous stems and are
northern winters or during the hot, dry adapted to short to relatively long peri
Mediterranean summers. The tuberous ods of dormancy. Most Asian species of
genera include Ambrosina, Arum, Bia AmorPboPballus occur in closed pri
rum, Dracunculus, Eminium and Heli mary or secondary forest undergrowth
codiceros. See Appendix II for ecological (van Alderwerelt van Rosenburgh, 1920,
requirements of these genera. Hu, 1968, Johns & Hay, 1981), but
T. Croat, 1988 9
sometimes also in open areas (see Ap Hook. f., Typhonium albispathum
pendix II). Bogner and Amorphophallus putii Gag
While some terrestrial aroids have nepain), but more commonly, species
relatively long, erect stems, the majority occur both on the limestone and on the
have short internodes and are tuberous trees growing over and in between
or rhizomatous. A few genera are re limestone rocks. In the neotropics, as
ported as cormose and there are differ well as in Asia, craggy limestone areas
ences of opinion as to whether they are are invariably good aroid sites, and
tuberous or cormose (see Colocasia, depending on the amount of rainfall in
Theriophonum and 1j;phonium in Ap the region and the exposure, they may
pendix II). Although standard definitions be species-rich sites as well. For exam
of corm and rhizome give distinct differ ple, in the region northeast of Tuxtla
ences (see glossary, Appendix III) it is Guttierrez in the state of Chiapas, Mex
not entirely clear how these are re ico, shady limestone cliffs may be the
flected in the Araceae. Engler (1905- only areas which are rich in species. The
1920) defines the stem types of Araceae area is relatively dry, and shady lime
in some detail (see especially the "Pars stone cliffs are substantially less arid than
Generalis," Engler, 1920), but he does tree trunks. Limestone rocks and granite
not include cormose as a stem type for boulders in forests are also important
Araceae. By the strictest definition of since they represent obstacles to normal
terms presented in a variety of glossaries tropical agriculture and are usually not
and textbooks there is no question that cleared to grow crops. Aroids in dis
genera like Amorphophallus produce turbed areas are thus more likely to be
tubers. It is less apparent from the found growing on rocks. Steep road
definitions of corms that this stem type banks also often have an established
exists among the Araceae. Two fairly aroid flora, presumably established soon
recent works have reported cormose after the roadcut was made and before
plants for the Araceae. These include the remaining forest in the region was
reports for Theriophonum (Sivadasan & cleared. The same situation exists for
Nicolson, 1982) and for Colocasia and epiphytic species which persist in deep
Typhonium (Pate & Dixon, 1982). ravines passed over by farmers (see
Burnett (1984) also mentions corm below).
production from the rhizomes of Aloca The epilithic habitat is as particularly
sia. The stem types mentioned in Appen important for rheophytes (see above
dix III have been taken from Engler under "rooted aquatics") as it is for
( 1905-1920) and also from the sources many genera which generally occur on
quoted in the text. For a few poorly the forest floor (see Appendix I). Many
known genera the stem type was de loosely-rooted species occur on the
duced from closely related genera. forest floor or along the edges of forest
just as commonly as on rocks. In Appen
3. Epilithic Plants
dix I, there are 18 genera (16% of the
Epilithic plants do not show a great total) classified as both terrestrial and
preference for the surface on which they epilithic and the percentage is possibly
grow. Many species grow as appressed much higher. The percentage of epi
plants on tree trunks or on boulders.
phytic genera which occur both on tree
Porous limestone is particularly suitable trunks and on rocks is higher still (see
for epilithic plants because of its ability below under "epiphytic plants").
to catch debris and to provide many
interfaces for adequate rooting sites. 4. Epiphytic Plants
Rarely is a species found only on lime Plants which are true epiphytes are
stone (e.g., Anthurium reflexinervium naturally restricted to growth on trees or
Croat sp. nov. ined., Colocasia gigantea shrubs and thus generally occur in
10 AROIDEANA, Vol. II, No.3
forests. They are almost invariably re juvenile plants of species which will
stricted to primary forest or regrowth in become large are found on shrubs,
primary forest, typically in humid to wet without the strong support needed for
areas, and commonly persist in large further development, but they rarely
trees, even after virtually all remaining persist there. Appressed hemiepiphytic
forest is removed, but in such cases they climbers such as Monstera, Pbiloden
often do not reproduce sexually. How dron, Rbodospatba and Syngonium re
ever, vegetative reproduction is so suc main in a juvenile or preadult condition
cessful in many epiphytic species that in shrubs since the right conditions of
they may become more abundant in adequate support and availability of light
such situations than they were in the are not met. The stems of such plants
primary forest. Even in primary forest commonly fall free after a time, return to
areas, sexually reproducing plants may the ground and seek a larger support.
be rare, while vegetative reproduction is Alternatively, some species of Antbu
very successful. For example, on Barro rium (e.g., A. kuntbii Poeppig, A. brevis
Colorado Island in Panama (Croat, padix Croat,A.pentaphyllum (Aubl.) G.
1978), some species, such as Monstera Don and A. flexile Schott) normally
dilacerata (K Koch & Sellow) K Koch occur on smaller trees, including small
and Syngonium erythrophyllum Birdsey palms, and on shrubs. Again the reasons
ex Bunting, are both rare as adults (only are not obvious, but they are species
one collection of an adult plant known which do not need to attain much height
for each on the island) while juvenile to flower and are generally small in
plants are abundant, in general found overall size. Pbilodendron section Ptero
throughout much of the trail system and miscbum also has species which appear
covering the ground virtually every to be restricted to shrubs, e.g., P. auran
where. tiifolium Schott andP. viaticum Croat &
Epiphytic plants, at least in their early Grayum sp. nov., ined.
stages of growth, show little preference
Most epiphytes (including hemiepi
for either rocks or trees ( commonly they
phytes) prefer to grow on the lower part
are referred to as epilithic, lithophytic or
of tree trunks, commonly from one to
rupicolous when occurring on the for
four meters above the forest floor, proba
mer). Most genera have been reported as
bly because conditions of light are gen
occurring on rocks, and those not previ
erally adequate and humidity is high.
ously reported as epilithic will probably
Perhaps even more important, the
prove to occur on rocks, at least in their
amount of available nutrients and water
initial developmental stages. Since all
increase toward the base of the tree, as
hemiepiphytic genera begin their devel
all nutrients for true epiphytes are de
opment in the soil (except a few species
rived from runoff from above. Not sur
of Pbilodendron which germinate on
prisingly, the only epiphytes which
trees and later produce roots which
occur very high in the canopy are
reach the ground), rocks or boulders are
unusual, either in their ability to with
often the first flat upright surface they
stand the effects of drought (e.g., with
encounter. Among climbing aroids there
thicker, generally more succulent leaves
are no known cases where rocks are
and/or roots ), or in their ability to
preferred to trees as the principal habi
acquire nutrients. Some members of
tat.
Pbilodendron subgenus Meconostigma,
Generally speaking, epiphytic plants for example, may grow very high in trees
prefer to grow on larger trees. The and eventually produce adventitious
reasons for this are unknown; perhaps roots which extend to the ground.
the perching behavior of birds dispers Antburium gracile (Rudge) Lindley
ing the fruits is the cause. Occasionally, often occurs high in the canopy, but
T. Croat, 1988 11
when found there it is generally associ little distinction made by most ap
ated with ant nests, which provide an pressed-climbing plants between rocks
alternate source of nutrients from detri and trees. However, appressed climbers
tus accumulated by the ants. It is also a are rarely seen on rocks, except at forest
species with roots having a velamen, edges or in open areas in the forest,
thus enabling it to better utilize atmos unless the rock is a very large one; this
pheric humidity as a water source. Some no doubt due to the unavailability of
members of Anthurium sect. Pachy light where smaller rocks occur. Alterna
neurium are capable of growing rela tively, along stream banks, rocks provide
tively high in the canopy or even on a more suitable habitat (permanency,
rocks in areas where there is little better drainage) than steep banks. The
overhead canopy to provide an adequate occurrence of appressed-climbing plants
nutrient supply. This group is ideally located there is much more frequent.
suited to conditions of low rainfall (and
Hemiepiphytic Araceae are of two
consequently low nutrient availability)
types. Primary hemiepiphytes, the first
and has short stems with a large, dense
type, are those which start their lives as
root mass, better able to catch rainfall
true epiphytes and later make connec
when it occurs and generally has rosu tion with the ground by means of long
late leaves to catch and hold fallen
roots which grow down from the plant
debris. The debris accumulates in the and make contact with the ground.
"basket" formed by the leaves and the Examples of this type are species such as
upper, younger roots grow into this Philodendron solimoesense A. C. Smith
debris, providing nutrients and water
and P. megalophyllum Schott.
holding capacity not available to most
The second type start their lives on
other epiphytic aroids.
the ground and climb trees where they
The epiphytic habit is perhaps even become adults and may lose their con
more diverse in form than the terrestrial nection with the ground. These are
habit, with both true epiphytes (those referred to as secondary hemiepiphytes
which never have contact with the (Putz & Holbrook, 1986). Most Anthu
ground), and hemiepiphytes (those rium and Philodendron species, as well
which rely on a support on which to as Anadendrum, He terops is, Poth
grow, but are also rooted in the ground). oidium, Pothos, Syngonium, many spe
True epiphytes may on occasion become cies of Cercestis, Culcasia and the tribe
hemiepiphytes by producing roots Monsteroideae are secondary hemiepi
which reach the ground, and hemiepi phytes.
phytes may become true epiphytes by
Most hemiepiphytes must attain a
losing their connection with the ground.
certain stem girth before assuming adult
The different classes of epiphytism will
growth and flowering. About half of all
be discussed in turn.
hemiepiphytes, including Allosche
4.1 Hemiepipbytes. This discussion of mone, Amydrium, Epipremnum, Mon
hemiepiphytes makes no distinction be stera, Rhaphidophora, Scindapsus and
tween plants occurring on trees and Syngonium, have heteroblastic leaf de
those occurring on rocks or on stones, velopment (leaf blades of radically differ
even though the term "epiphytes" re ent shapes at different stages of develop
fers specifically to the former. Perhaps a ment). One of the most radical examples
new term needs to be coined, such as of heteroblasty occurs in Monstera
"hemiepilythiphytes", to describe where some juvenile leaves (sect.
plants using rocks as their support but Marcgraviopsis) are tightly appressed
which are rooted in the ground. From ("shingle leaves") and others are free
the standpoint of the plant (as already and spreading. In time, this growth form
mentioned above) there seems to be gives way to intermediate, pre-adult
12 AROIDEANA, Vol. 11, No.3
leaves which are more nearly shaped like especially vines, often occurring in the
the adult blades, but which usually are canopy of the forest (e.g., P. davidsonii
entire, not perforate or lobed (see pho Croat and P. scandens K Koch & Sel
tographs). Higher up on the stem adult low). Cercestis and Culcasia often
leaves are later formed. This generally flower very near the ground, as do
means genera with heteroblastic leaf Anadendrum, Pothoidium and Pothos.
development must attain a suitable Spathiphyllum commutatum Schott,
height on the tree trunk (generally 2.5 to and S. solomonense Nicolson, both of
5 m) to pass through the juvenile and which may be hemiepiphytic, flower
preadult phases. Light availability ap near the ground.
pears to be the most important criterion Internode length plays an important
for a plant converting from juvenile to
role in defining growth behavior of
preadult leaves (Ray, 1987). Adult plants
epiphytes, especially hemiepiphytes.
may flower even on short tree stumps in
Among hemiepiphytes, there are rela
forest regrowth, or on rocks in open
tively few vines or plants that are
areas. Substrate is equally important
markedly scandent. Species generally
since some plants, under greenhouse
have relatively long internodes when
conditions with adequate light but with
they are young and in an establishment
out adequate support, have never been phase. As the plant approaches maturity,
observed to change to their adult forms. internodes become shorter and thicker.
Even if a concrete wall of adequate The transition may be fairly abrupt, but
height (5 meters or more) is provided, generally occurs over a long succession
some species grow upon the wall end of internodes. Once sexual maturity is
lessly without becoming adult plants. reached, and assuming no such major
disruptions as a treefall (which will
Species of hemiepiphytes that do not
greatly affect the available light or the
undergo heteroblastic development
plant's disposition), most plants indefi
have leaves which become increasingly
nitely produce short internodes which
larger in size as the plant matures, but do
grow slowly up the side of their support.
not undergo marked changes in leaf
There are a number of exceptions to this
morphology. Commonly, however, there
rule. Some species ofP hilodendron, e.g.,
are minor differences in shape and often
P. linnaei Kunth, produce a series of
coloration and texture as well. The
short internodes with a tight rosette of
non-heteroblastic genera of hemiepi
leaves alternating with a series of long
phytic aroids include Anadendrum,
internodes, which carries the plant apex
Cercestis, Culcasia (both of the latter
higher up the tree where another rosette
sometimes merely terrestrial), Heterop
ofleaves is produced (Blanc, 1980). This
sis, some Monstera, Philodendron, Poth
process can be repeated indefinitely.
oidium, Pothos,Rhodospatha and Spath
Philodendron /ragrantissimum (Hook.)
iphyllum (the last almost always ter
Kunth has the same manner of growth
restrial ). The height at which these
but its rosettes are more widely spaced
genera reach flowering size varies
and are even sometimes found on differ
greatly, but is generally much lower than
ent trees.
those genera with heteroblastic develop
ment. Rhodospatha usually flowers at Other important exceptions to the
heights similar to those of heteroblastic rule that hemiepiphytes remain in the
genera (above 2.5 m), while Philoden "short internode stage" once they have
dron is variable, with some species reached this developmental stage are
flowering near the ground or even on those exhibiting heteroblasty (Syngo
terrestrial plants about one meter above nium and genera in the tribe Monsteroi
the forest floor (e.g., P. luteynii Croat & deae). These genera have the ability for
Grayum, sp. nov. ined.) and others, repeated conversions from adult growth
T. Croat, 1988 13
with short, thick internodes to juvenile preadapted for such conditions; they are
growth with long, slender internodes often much more abundant in weedy
(Ray, 1983a, 1983b, 1986, 1987). habitats.
Scandent hemiepiphytes begin their The same situation often applies to
growth in usually the same manner as areas where part of the forest has been
short stemmed appressed-climbers, but cut away, such as a new road. Most
differ in that the production of longer hemiepiphytes thrive particularly well in
internodes continues perpetually. As the these partially-shaded forest edges.
plant matures, the stems usually also Open areas along rivers and smaller
increase in diameter with only moderate streams offer similar growing conditions.
decrease in length of internodes. The neotropics have a much higher
On appressed-climbers, usually only percentage of hemiepiphytic genera that
the uppermost nodes (commonly fewer are than do the paleotropics. Of all the
than ten) are leaf-bearing, but much of genera which are predominantly epi
the non-leafy stem is intact and acts as phytic, only Stenospermation is never
continued physical support and proba hemiepiphytic. Anthurium, though it
bly will also have still active roots for has numerous terrestrial species and a
absorbing water and nutrients. The most few hemiepiphytic members, largely
active roots are always borne on the consists of true epiphytes. Philodendron
leafy portion of the plant. However, is largely hemiepiphytic, with only a few
hemiepiphytic vines are leafy through true epiphytes which start their lives as
out all or much of their length and their epiphytes and remain epiphytic (e.g., P.
roots are likewise more scattered and wendlandii Schott and P. davidsonii
occur only at the nodes. They are not Croat).
aggregated in a manner allowing debris In contrast to the American tropics,
to be easily trapped among them, and are Africa and the Malagasy region have no
therefore less successful in providing true epiphytic genera (Remusatia is
themselves with a nutrient supply. Per sometimes epiphytic in Asia and Ma
haps for this reason the number of dagascar) and only four hemiepiphytic
hemiepiphytic vines is relatively low genera: Cercestis and Culcasia (en
compared to the number of appressed demic), Pothos and Rhaphidophora,
epiphytes. Still, it cannot be denied that which are indigenous but better repre
many hemiepiphytic vines (e.g., Philo sented in Asia.
dendron scandens K. Koch & Sellow, Four epiphytic genera occur in Aus
Epipremnum pinnatum (L.) Engl. and tralia: Epipremnum, Pothos, Pothoid
Pothos scandens L.) are among the most ium and Rhaphidophora. All are hemi
widespread and successful species.
epiphytes. The percentage of hemiepi
In the New World all of the hemiepi phytes in the Australian flora is rather
phytic genera occur principally in pri high (five out of 17). All Australian
mary, mostly humid to wet forests. genera (and most of the species as well)
These genera include Alloschemone, except Gymnostachys, are widespread
Anthurium (few species), Heteropsis, in Asia. Asia has eight indigenous genera
Monstera, Philodendron, Rhodospatha of epiphytes, and all are hemiepiphytic.
and Syngonium. Some species, espe These include Amydrium, Anaden
cially of Monstera and Syngonium and drum, Epipremnum, Rhaphidophora,
also of Philodendron, may be abundant and Scindapsus. Spathiphyllum com
in weedy situations, commonly along mutatum Schott (based on Croat 33032)
fence rows and on trees in coffee has been observed as an incidental
plantations. In natural habitats they gen hemiepiphyte in the Philippines. Most
erally begin their growth in areas of are members of the understory or they
natural disturbance and so are occur along primary forest edges or in