Study Notes on Palmae (Aricaeae) | Monocotyledonae

The below mentioned article provides a study notes on Palmae.

Palmae are perennial woody plants with stout un-branched stem leafy at the top; some are very tall while a considerable number is dwarf and some are scrambling; a short horizontal rhizome is often formed which later becomes ascending and grows to an erect cylindrical stem. The primary root perishes early and a tuft of adventitious roots arise around the base of the stem.

The leaves are of 2 types, palmately or pinnately com­pound and those with the former type of leaves are called Fan-palms and others are the Feather-palms; simple palm type of leaves also occur which are usually deeply cleft; leaves are usually very large and long-petioled, crowded only at the apex to form a dense crown; in the case of scramblers the leaves ate alternately scattered over the stem; the petiole is usually woody and clasping the stem at the base and sheathing in some genera; the falling leaves leave ring-like scars on the stem or the leaf-bases remain attached to the stem and the leaves break and fall off on drying due to their own weight.

Ochreate stipule is present in some cases, particularly in the scramblers and in Korthalsia scaphigera Mart, the ochrea form a hollow chamber where the ants take shelter.

The inflorescence is usually a large compound spadix enclosed primarily in one or more large bracts or spathes which split longitudinally and the panicle grow out exposing the flowers; the bracts are often hard and woody; the inflorescence may appear from the axils of the leaves or from the axils of fallen leaves, i.e. below the crown of leaves; rarely the inflorescence is terminal and in this case appears only when the life cycle of the plant comes to its end as in Corypha and Metroxylon; such are called monocarpic palms that die after producing flower and fruit once in their life time.

Flowers are unisexual very rarely bisexual and the plants are usually monoecious, rarely dioecious, e.g. Phoenix, Borassus and Lodoicea.

The numerous small flowers are sessile and are often embedded in the fleshy axis of the spadix, spirally arranged or are distichous; the female flowers may occupy the lower portion of the spadix or its branches and males are on the upper portion or both may be mixed; in Geonoma flowers are in groups of three on the spike, each group having a female flower between 2 males.

Flowers are regular, with 2 whorls of perianth; segments 3 in each whorl, persistent, free or connate, coriaceous, similar or the inner larger, thicker and tougher. Stamens 6 in 2 whorls, free, rarely united at the base and very rarely slightly adnate to the base of inner perianth-segments; sometimes one whorl of stamen is wanting and there are only 3 stamens, e.g. Nypa ; or there are many stamens as in Caryota, Pinanga and a few other genera; anthers 2-locular with great quantities of powdery pollens.

Ovary supe­rior, tricarpellary, united, 3-celled or 1 -celled with one ovule in each cell; rarely carpels partially or completely free; style absent or short with a trilobed or tripartite stigma; 2 of the 3 carpels often become abortive so that the fruit is one seeded.

The fruit is a berry or a drupe with 1-3 seeds; the embryo very small, embedded in soft or cartila­ginous or horny endosperm which is often ruminated. The fruit is often covered with imbricating scales. The flowers are wind pollinated except in the case of a few genera, e.g. Sabal, Chamaedorea, etc. which are entomophyllous. Self-pollination is prevented even in bisexual flowers as they are protandrous.

The germination of seed in this family is of a bit different type. The cotyledon elongates in the form of a tube and pushes out the radicle and hypocotyl. The tube enters the ground while the seed remains above. The radicle or the tap root gives out several branches in a very short time and then the tap root perishes.

The plumule pierces the enclosing cotyledonary sheath and the first leaf emerges. The end of the cotyledon remains inside the seed forming a sucker and absorbing the food material reserved in the endosperm. The cotyledonary tube is often as long as 30 cm as has been noticed in Hyphaene and Borassus.

The sucker may grow to a large size as in Cocos nucifera Linn, or in Borassus. The seedling before producing a green leaf produces 1-3 pale greenish yellow sheaths only. The green leaves that follow are: at the beginning simple and narrowly lanceolate or with broader blade deeply incised from the apex.

The stem elongates very slowly, increasing all the time in circumference, and as the larger leaves are produced one after another the stem takes the shape of an inverted cone due to the pressure imparted by the leaf-bases. With the production of a dense whorl of normal leaves the stem comes above the ground and grows erect to form the cylindrical trunk.

The family comprises about 217 genera and about 2500 species. They are mainly distributed in the tropical and subtropical parts of the world. Chamaerops humilis Linn, is the only species found wild in southern parts of Europe. On the east palms have reached the northern limit in Korea and S. Japan while in the south they have been found to grow in Australia.

In the Himalayas ‘Trachycarpus martiana Wendl has been found to grow at an altitude of 2000 mtr. or even at higher altitude. Calamus floribundus Griff., Plectocomia himalayana Griff, also occur at almost that height. Nannorhops with its single species N. ritchieana Wendl is found from the Western Himalaya to E. Persia through Afghanistan.

On the New World palms occur as far north as California and as far south as Chili. The tall palms prefer bright sun while a few dwarf species grow well in shade under cover of large trees of the tropical forests. Phoenix paludosa Roxb. is a mangrove plant and form almost pure associations in open areas in the littoral forests on the banks of the creeks.

Nypa fruticans Wurmb. is another palm of the mangrove forests. Few palms grow in arid regions. Hyphaene thebaica Gaertn is found in North Africa and H. indica Bece occurs in Gujrat of India. Phoenix dactylifera Linn, grows, all over N. Africa and the W. Asiatic countries and brought to India by the Muslims in the 8th or 9th century.

It is now cultivated in some parts of southern Europe. Fossils of palms have been discovered in Europe as far north as 50° latitude or more. These are believed to be of Cretaceous period. This proves that the family had a wider distribution in past.

Variation:

Variation occurs both in vegetative as well as in floral parts. There are the erect forms and the scrambling forms. The erect forms have un-branched stem except the Hyphaene or the Doum palm where the stem forks several times. Phoenix sylvestris L. and Chrysalidocarpus lutescens Wendl. often produce branches as a result of injury.

In some genera the leaf-sheaths are long and stem clasping e.g. Areca, Roystonia, etc. while in Phoenix, Borassus and a few others the sheath is not perceptible but the leaf-base is stem-clasping. The leaves drop off leaving the scars on the trunk, but in Phoenix and Elaeis the leaves break off from the middle of the petiole and the trunk is covered from top to bottom with leaf-bases and the basal part of the petioles.

Usually the palms are unarmed but quite a number of them especially the scrambling or clim­bing ones are armed with spines or thorns. The scrambling forms are stipulate. The ochreate stipules are in the form of long tube and often have a whip-like structure at the apex which is called “flagellum”.

In these palms the leaf rachis also ends in a flagellum. The flagella help in climbing. Palms are polycarpic excepting a few genera which are monocarpic, e.g. Corypha, Metroxylon. The species of Arenga behaves pecu­liarly at the time of flowering; a plant grows to a height of about 8 mtr. or more in course of 10-12 years.

Then an inflorescence comes out on one side below the crown of leaves. Next year another spadix comes out on the opposite side a little below the first one. This is repeated until the last spadix comes out very near the ground. After the last spadix ripens its fruits the palm dies and stands for some-time like a hollow cylinder.

In this family flowers are unisexual but bisexual flowers occur in Livistona, Licuala, Trachycarpus, etc. In the genera Phoenix, Borassus and Lodoicea the plants are dioecious while in other genera they are monoecious.

The inflorescence is usually a branched panicle but in Borassus it is a simple spike. In some genera a large spathe encloses the young inflorescence and in others there are several each enclosing a branch of the panicle.

In monoecious plants female flowers are generally arranged at the based part of the spike and the males are above them. In Geonoma male and female flowers are inter­mixed. The perianth segments are similar in both whorls and are free. In Areca the inner segments are much larger; in Borassus the inner 3 are shorter than the outer.

In Wallichia the inner segments unite to form a 3-partite corolla. The stamens are usually 6 and free. In Nypa there are only 3 stamens and in Pinanga, Caryota and a few others there are many. In Roscheria and Elaeis they are united in a ring. Carpels are 3 and usually form a trilocular ovary, rarely they are more or less free, e.g. Phoenix.

In Pinanga, Areca, etc. the ovary is I-celled. In Cocos 2 of the carpels become abortive in course of fruiting. The ovules are generally anatropous and rarely orthotropous. Fruits are berries or fibrous drupes which in the tribe Lepidocaryeae are covered with imbricating scales. Some species have very large fruits, e.g. Borassus flabelifer Linn, Cocos-nucifera Linn, and Lodoicea maldivica (Gmel) Pers.

The last looks like 2 large-sized coconuts glued together. The berries of Euterpe, an American genus, are on the other hand a little bigger than the pea.

The seeds also vary in size and shape; they are more or less rounded as in coconut, Corypha, etc., compressed as in Borassus, Nypa, etc., oblong or linear in Phoenix, where it is longitudinally furrowed. The endosperm may be soft containing oil and protein or may be hard and rarely mucilaginous. In some cases the endosperm is ruminate, e.g. Areca, Caryota, etc.

Affinity:

Palmae is closely related to Araceae. Engler and Hutchinson put the family in a monotypic order while Rendle includes this family in Spadiciflorae along with Araceae and Lemnaceae.

Hutchinson considers it to be allied also to Pandanaceae on one side and Agavaceae on the other and thinks that from the latter it probably origi­nated. Takhtajan and Cronquist consider that Agavaceae is more recent than Palmae (Arecaceae) which is in the subclass Arecidae while Agavaceae is in Liliidae.

So ac­cording to them Palmae is more primitive to Liliaceae and allied families and in this respect they agree with Engler. However, the unisexual inconspicuous flowers borne in spadix are characters found in both the families of Palmae and Araceae and this suggests that the two are closely related.

Then the perianth in 2 trimerous whorls, six stamens and superior trilocular ovary bring Palmae closer to Liliaceae and more so to Agavaceae of Hutchinson having Woody plants like Yucca and Dracaena.

Economic Importance:

The family contains many plants which are very much important economically.

A few species are noted below:

Cocos nucifera Linn:

No other species in the vegetable kingdom is perhaps more useful than this one. It supplies food and drink from the endosperm which also yields edible oil valued for soap manufacture. The fibrous coat of the fruit is used for manufacture of ropes, for “choir-matting and for stuffing cushions.

A sugary juice is obtained by tapping the inflorescence. The shell of the fruit is used for manufacture of buttons. The trunk is used as posts in house-building and also as fuel. The stiff mid­ribs of the leaflets are used to make brooms.

The tender leaflets are woven into baskets or mats. The dry leaves and parts of the dried spadix are also used as fuel. The genus Cocos have 30 species under it of which all are confined to C. America excepting C. nucifera L. which is widely distributed in tropical Asia.

Metroxylon:

M. rumphii Mart, and M. sagu Rottb of Malaya yield sago from the starch obtained from the pith of the stems. Mauritia flexuosa L.f. (America) also yields sago of good quality. It may be mentioned here that sago is also manufactured from the pith of Cycas species and from the starch obtained from the tuberous roots of Manihot esculenta Crantz (Euphorbiaceae) which is now cultivated in S. India for that purpose.

Phoenix:

P. dactylifera Linn, is the Date palm indigenous to Arabia and N. Africa and is found in cultivation in W. Asia and S. Europe. Cultivation of Date palm started in Arab-countries as early as 3,000 years before Christ. It was brought to India by the Muslim settlers. P. sylvestris Roxb is the wild date of India and yields copious sugary juice by tapping from which a kind of molasses and a country liquor are pre­pared.

Borassus:

B. Flabelifer Linn, the single species of the genus also yields copious sugary sap from the peduncle when the spadix is cut down. The mesocarp of the fruit has a sweet pulp along with the fibres and is much relished. The soft endosperm of seeds of the immature fruits is also edible as well as the end part of the cotyledon that remains inside the seed as a sucker.

The leaves are made into fans and the trunk is used as posts and rafters in house-building. The trunk is also hollowed to make a dug-out canoe. All parts of the tree properly dried are used as fuel. This species is considered to be indi­genous to central Africa wherefrom it has come to India and growing freely.

Areca catcchu L. is the Betlenut, cultivated in India and other east Asiatic countries.

Elaeis guinensis Jacq. is the African oil-palm, the fleshy mesocarp of the fruit of which yields an edible oil.

Phytelephas macrocarpa Ruiz. & Pav. is the source of vegetable ivory. It is indigenous to tropical America.

Copernicia cerifera Mart, of the Amazon region and Ceroxylon andicola H. & B. of the Andes yield Carnauba wax exuded from the leaves.

Calamus:

Different species of the genus supply cane of good quality for chairs, baskets, walking sticks, etc. and are Indo-Malayam.

Many palms are grown in gardens as ornamentals, e.g. Chamaerops humilis Linn., Raphis flabelliformis Act., R. humilis Bl., Licuala. paludosa Griff, L. elegans Bl., L. grandis Wendl., Livistona chinensis R. Br., Chrysalidocarpus lutescens Wendl., Ch. madagascarietisis Becc., Roystonia regia (Kunth) Cook, Ptychosperma macartheri Wendl. Pritchardia species, etc.

Subdivisions of the family: Within the family Drude recognises 6 subfamilies which fall into 2 groups:

A. Perianth well-developed, enclosing the fertilised ovary.

I Coryphoideae —Spadix loosely branched; flowers scattered, not in groups, often in rows, uppermost opening first; carpels 3, free or united at first. Tribes— Phocniceae and Sabalae.

II Borassoideae—Spadix simple or little branched, branches stout and cy­lindrical; flowers markedly diclinous-dimorphic, subtended by bracts; the males in cincinus in grooves of the branches; carpels 3, united. Tribe—Borassieae.

III Lepidocaryoideae—Spadix branched, often in 2-ranked manner; flowers in cincinni or 2-ranked spikes, subtended by bracts and bracteoles; carpels 3 united, covered with scales. Tribes—Mauriticae and Metroxyleae.

IV Arecoideae—Spadix simple or branched; flowers diclinous, usually dimorphic, when dioecious solitary and scattered on spikes with rudimentary bracts, when monoecious in cymes of 3, 2 being males and one female, or one female at top of the spike with several males below; carpels 3, united, ovary 1-3 celled.

B. Perianth rudimentary; fruits in dense heads.

V Phytelephantoideae—Stamens many, free; female flowers with perianth— 1 genus—Phytelephas.

VI Nypoideae—Stamens 3, united below; female flower naked—1 genus— Nypa.