FBS 204: Architecture of Tropical Trees
Exercise 1
The Initiation of the Tree: Germination and
Seedling Morphological Types
Reyes, Philip Jones G.*
Introduction
The life of a tree begins with the germination of the seeds and the emergence of the
seedlings. Lexically, a seedling is defined as “a young plant grown from a seed” (MerriamWebster’s Dictionary), therefore emphasizing its distinction as a sporophyte resulting plant
through sexual reproduction. The initiation of a tree begins with the seedling stage making this
stage obviously essential on a plant’s life cycle. The seed and seedling stages generally exhibit the
peak of mortality rates among all plants in comparison to other life stages of seed plants (Halle, et
al., 2012).
Seedling morphology is probably one of the least studied facets of botany which is why
there are only two widely recognized types of germination: epigeal and hypogeal. These two
divisions are distinctly divided based on the positioning of the cotyledons upon seed germination.
Epigeal germination is exhibited by seedlings with cotyledons positioned above the ground while
hypogeal germination is its opposite, when cotyledons remain subterranean. Nonetheless, with the
increasing knowledge and observations on seedlings, other seedling morphological types have
emerged having specific distinction from being just hypogeal or epigeal (Duke, 1965, Ng, 1973
and Burger, 1972 from Halle, et al., 2012). Such germination types are the semi-hypogeal type and
the ‘durian’ type.
By the end of the exercise, the following objectives must be met by the students:
1. To study and describe seedling tree architecture
2. To characterize the different seedling germination type; and
3. To assess and determine the importance of the different germination types.
Review of Related Literature
The most basic classification of tree seedling architecture is provided by Ng in 1978 in his
article “Strategies in Establishment of Malayan Forest Trees”. He came up with four general
seedling architectural types namely, epigeal, hypogeal, semi-hypogeal and ‘durian’ type. Different
factors were considered in establishing the boundaries between these types specifically, position
of the cotyledon, tendency of the cotyledons to be photosynthetic, exposure of the cotyledons
[phanerocotyly (exposed) or cryptocotyly (unexposed)] and the length and functions of the
hypocotyl.
Seedling that exhibit epigeal germination has photosynthetic phanerocotyl found above the
ground. This is the most common type of germination which is often associated to species with
small seeds. Since the cotyledons of these species are ought to be photosynthetic, it is expected
that they must be emerged and exposed to the sun. Hypocotyl in this type is therefore developed
*MS in Forestry: Forest Biological Sciences, Department of Forest Biological Sciences
FBS 204
well. Most of the species with this type of germination have seeds that are small in size (>3mm)
(Ng, 1978). On the other hand, hypogeal germination, opposite of the former, has unexposed nonphotosynthetic cryptocotyl which remain buried underground. Since the seed body remains rested
on the ground if favors the development of a bulky storage tissue, the endosperm. The hypocotyl
is undeveloped. This germination type is common in palms.
Fig. 1. Germination types proposed by Gatin (1904). A. Remote
tubular (Phoenix). B. Remote ligular (Sabal). C. Adjacent ligular
(Phoenicophorium). Source: Uhl & Dransfield, 1987 from
Henderson, 2006.
In fact, Henderson (2006) examine seedlings of palms and agreed to Gatin’s proposal of
the three more specific hypogeal germination manners of the Arecaeae family with respect to the
distance and connection of the seed bodies (reserves) to the plant. Gatin’s classifications were
remote tubular, remote ligular, and adjacent ligular (shown in Fig. 1 A, B and C, respectively).
Cotyledons of hypogeal seedlings are not photosynthetic, therefore exposure to the sun by
emergence to the seed coat and lifting from the ground is not needed. Hypogeal seedlings usually
produce ‘cataphylls’, small, scale-like leaves which are usually present on the lowest nodes (Ng,
1978).
The semi-hypogeal type of germination is clearly an intermediate between the first two
types. The cotyledons remain lying on the ground, often with seed coats still adhering
(cryptocotyly). Since, the cotyledons’ weight does not need support from the plant, it can develop
storage tissue. Photosynthetic cotyledons are not common.
The last type according to Ng (1978) is the ‘durian’ type, attributed to Durio zibethinus L.,
which is the model of this type. Durian type of germination is found in seedlings with unexposed
(cryptocotyl, still attached seed coat) cotyledons above ground. This germination type is baffling
as it is somehow disadvantageous since the energy is utilized in lifting the non-photosynthetic
cotyledons which then will be shed later without being even exposed. Some species however
compromise this disadvantage by elongating their epicotyls.
Architecture of Tropical Trees
On a study by Ibarra-Manriquez et al. in 2001, he used the seedling morphological types
by Garwood (1996), similar with Ng the only distinct difference however is the specificity of the
type of cotyledons in the epigeal type. He divided the epigeal type into two; phanerocotylar epigeal
with foliaceous cotyledons and phanerocotylar epigeal with reserve cotyledons. Nonetheless, the
positioning and exposure of the cotyledons are still the major differences.
Methodology
The students were tasked to scour specific areas inside the Makiling Botanic Gardens,
College of Forestry and Natural Resources, University of the Philippines- Los Baños and look for
five seedlings of different forest trees. All the four general germination types must be exhibited by
the seedlings documented in the field. When a particular seedling is documented, it is
photographed onsite and uprooted. The uprooted seedlings were then photograph in front of a clear
background. Line drawings of the uprooted seedlings were also generated with labels of the
recognizable seedlings part and emphasizing the germination type.
Results and Discussion
Photographs of the standing and the uprooted seedlings are shown in figures 2-6, as well
as their labelled line drawings. The species that were included in the exercise were Magabuyo
(Celtis luzonica Warb.), Amugis (Koordersiodendron pinnatum (Blanco) Merr.), Anubing
(Artocarpus ovatus Blanco), Panau (Dipterocarpus gracilis Blume) and one seedling of an
unidentified Areca spp.
FBS 204: Architecture of Tropical Trees
Celtis luzonica Warb.
(Cannabaceae)
Fig 2. Seedling of Magabuyo (Celtis luzonica.) (a) standing, (b) uprooted and (c) line drawing
The seedling of Celtis luzonica evidently shows epigeal type of germination. Specifically,
phanerocotyl epigeal with reserve cotyledons (PER) due to the bulkiness of the cotyledon found
above ground without the adherence of the seed coat. The hypocotyl is conspicuous.
*MS in Forestry: Forest Biological Sciences, Department of Forest Biological Sciences
FBS 204: Architecture of Tropical Trees
Koordersiodendron pinnatum (Blanco) Merr.
(Anacardiaceae)
Fig 3. Seedling of Amugis (Koordersiodendron pinnatum) (a) standing, (b) uprooted and (c) line
drawing
Koordersiodendron pinnatum seedling shows a cryptocotylar epigeal type of germination or in
Ng’s classification, the Durian type. The Durian type is a modification of the common epigeal type. The
cotyledon reserves obviously are above ground; however it remains cryptic and still is unreleased from its
testa. The hypocotyl is clearly visible. After some time, the seed body (the seed coat plus the tissues inside)
will fall when the leaves can photosynthesize sufficiently. Ng (1978) classified K. pinnatum as ‘durian
type’.
*MS in Forestry: Forest Biological Sciences, Department of Forest Biological Sciences
FBS 204
Artocarpus ovatus (Blanco)
(Moraceae)
Fig 4. Seedling of Anubing (Artocarpus ovatus.) (a) standing, (b) uprooted and (c) line drawing
The third seedling, the Artocarpus ovatus seedling on the other hand exhibits a hypogeal type of
germination, particularly cryptocotylar hypogeal type. The seed coat remains intact not exposing the seeds
and the cotyledon reserves are found underground. Species under the genus Artocarpus such as A.
heterophyllus and A. altilis are reported to have hypogeal type of germination as well (Khan, 2003 and
Deivanai S. & Bhore, 2010). In fact, Schmidt (2000) reported that the genus Artocarpus exhibit the
hypogeal type of germination. The hypocotyl of the seedling is not developed.
Architecture of Tropical Trees
Dipterocarpus gracilis (Blume)
(Dipterocarpaceae)
Fig. 5. Seedling of Panau (Dipterocarpus gracilis) (a) standing, (b) uprooted and (c) line drawing
Panau (Dipterocarpus gracilis) seedling shows durian type of germination. It is such because of
the cryptic behavior of the above ground cotyledons. In fact, the whole fruit (pericarps and wings) is still
enclosing the cotyledon reserves. Ng (1978) noted that some Dipterocarpus species have durian type of
germination (D. alatus, D. grandiflorus and D. validus). Schmidt (2000) reported that Dipterocarpus spp.
are durian type.
FBS 204
Areca sp.
(Arecaeae)
Fig. 6. Seedling of Areca sp. (a) standing, (b) uprooted and (c) line drawing
The seedling of this monocot clearly shows a hypogeal type of germination (cryptocotylar
hypogeal with reserve cotyledons) as the seed body, both seed coat and cotyledons (and endosperm) are
subterranean. The hypocotyl is undeveloped.
Findings
Following Ng’s morphological seedling architectural types (1978) the five species only showed
three of them: epigeal, hypogeal and the durian type. No seedling was found to show semi-hypogeal type
of germination. Based in available literature, semi-hypogeal type of germination is exhibited by Gmelina
elliptica, Milletia spp., Erythrina spp., Pithecellobium spp., Amoora sp. Chisochenton pentandrus,
Architecture of Tropical Trees
Sympetalandra densiflora, Palaquium philippense and Allium cepa (Ng, 1978; Schmidt, 2000).
Unfortunately, no seedlings of these species were observed in the area given.
During the conduct of the exercise, majority of the seedlings observed were epigeal. Seedling of
Pterocarpus indicus, Sandoricum koetjape and Diplodiscus paniculatus (Figure 7) are among the
observed epigeal seedlings during the exercise. Epigeal germination is known to be the most common
type in woody plants. All gymnosperms, and the major families of angiosperms have epigeal germination
(Schmidt, 2000).
Fig 7. Epigeal Seedlings of Diplodiscus paniculatus (A) and Sandoricum koetjape (B)
On his study on the seedling morphological types of Malayan forest trees, Ng (1978) noted that
64% of the species exhibit epigeal type of germination (hypogeal: 18%, semi-hypogeal: 10% and durian:
8%). These results are also partly reflected by Makiling forest trees based on a study by Fernando (1980)
with epigeal germination accounting for 80%. The lowest however is the semi-hypogeal type with only
3% (hypogeal: 7% and durian: 10%). Another study by Ibarra-Manriquez et al. (2001) showed that
Mexican forest trees also have the highest percentage of epigeal germination (both foliaceous (49.5%) and
reserve cotyledons (9.5%)) with 59%. Hypogeal germination accounts for 31.4%; durian type has 2.4%
and semi-hypogeal has 7.2%. These statistics from tropical rain forests seem to be the reason why majority
of the seedlings observed in the field were epigeal.
In summary, Magabuyo seedling is an example of epigeal type of germination with reserve
cotyledons (which perhaps are photosynthetic due to its green color) while, Amugis and Panau seedlings
show the durian type of germination with epigeal cryptocyl that are non-photosynthetic. Amugis and
Panau seedlings’ cotyledons remain attached from their seed coats. The former species’ seedling all
developed hypocotyls. Lastly, Anubing and Areca spp. seedlings exhibit hypogeal type of germination
evidence by their cotyledons being unexposed and subterranean and undeveloped hypocotyl.
FBS 204: Architecture of Tropical Trees
References:
Burger, D. 1972. Seedlings of some tropical trees and shrubs mainly of South East Asia. Centre for
Agricultural Publishing and Documentation (PUDOC), Wageningen,
De Vogel, E.F. 1980. Seedlings of Dicotyledons: Structure, Development, Types, & Descriptions of 150
Woody Malesian Taxa. 465p. PUDOC, Wageningen.
Fernando, E.S. 1980. The Identification of Seedlings of Some Commercial Timber Trees on Mt. Makiling,
Luzon Based on Morphological Characters. 132p. MSc Thesis, University of the Philippines- Los
Baños, Philippines.
Fernando, E.S. 2011. Seedling establishment in tropical rain forests: understanding the evolutionary
strategies, paper presented to the Green Monday Rain Forest Restoration Initiative Seminar Series,
Intitute of Biology-
University of the Philippines Diliman, 05 September 2011.
http://www.rainforestation.ph/news/pastEvents/greenMondays_Jun2011Feb2012.html
Hallé, F., Oldeman, R.A. and Tomlinson, P.B., 2012. Tropical trees and forests: an architectural analysis.
Springer Science & Business Media.
Henderson, F. 2006. Morphology and Anatomy of Palm Seedlings. The Botanical Review 72 (4): 273-329.
The New York Botanical Garden, New York, U.S.A.
Ibarra-Manriquez, G., M. Martinez Ramos, & K. Oyama. 2001. Seedling functional types in lowland rain
forest in Mexico. American Journal of Botany 88(10):1801-1812.
Ng, F. S. P. 1978. Strategies of Establishment in Malayan trees. In Tomlinson, P.B. & M.H. Zimmerman
(eds.), Tropical Trees as Living Systems, pp. 129-162, Cambridge University Press, Cambridge,
U.K.
Schmidt, L. 2000. Guide to Handling of Tropical and Subtropical Forest Seed. Danida Forest Seed Centre.
Royal Veterinary and Agricultural University (KVL), Denmark.
*MS in Forestry: Forest Biological Sciences, Department of Forest Biological Sciences