In this article we will discuss about autotrophic and heterotrophic plants.
Autophytes or Autotrophic Plants:
These plants are able to produce their own food.
These are mainly of two types:
(a) Photo- trophic plants, and
(b) Chemotrophic plants.
(a) Phototrophic Plants:
These plants can produce their own food through photosynthesis by utilising light energy – mainly from the sun trapped by chlorophyll, water from soil and CO2 from air. The common green plants and epiphytes belong to this category.
The epiphytes are the plants which remain attached to other plants mainly for mechanical support and not for nourishment. They are entirely cut off from soil contact and adopt various contrivances to absorb and retain atmospheric moisture and rain water for future use.
1. Some plants, like orchids (Vanda rox- burghii, Dendrobium nobile etc.) develop a special type of water-absorbing tissue ivelamen) on the outer surface of the aerial roots, which can absorb and retain water for future use. Another type of roots (clinging roots) are present in Orchids to get attached firmly with the host plant (Fig. 1.10A).
2. In some other orchids, ferns like Asplenium nidus, etc., some receptacles are formed by the leaves or aerial roots which collect humus and other material and get spongy. This receptacle with spongy substratum acts as reservoir to retain water and the absorbing roots derive water with nutrients from it.
3. In Dischidia rafflesiana (Fig. 1.10B, C) of Asclepiadaceae, the storing and constant supply of water is being performed by the pitcher-like leaves developed at the nodes. Rain water is collected inside the pitcher. This water is being absorbed by the much-branched adventitious roots.
(b) Chemotrophic Plants:
Bacteria are the plants that can produce their own food by utilising chemical energy. These include iron bacteria, sulphur bacteria, nitrifying bacteria, etc.
Heterophytes or Heterotrophic Plants:
These plants are not able to produce their own food and depend on others for food.
These are mainly of two types:
(a) Parasites, and
Some plants, which derive nourishment from other plants or animals are the parasites. The plant on which parasite grows is called host. When the parasites are usually confined in the roots of the host, they are called root parasites, and, on stem, called stem parasites. A close relationship exists between the host and the parasite.
Depending on the degree of parasitism, it is of two types:
1. Total parasites or holoparasites. Sometimes the parasites may be wholly dependent on the hosts, there are total parasite or holo- parasite. The parasites draw the nutrition from the host by root-suckers (haustoria) or by parasitic roots, those establish connections with their food conducting channels i.e., the phloem. It is of two types Root parasites and stem parasites.
i) A leaf-less root parasite without any chlorophyll, e.g., Balanophora dioica (Fig. 1.11 A) of Balanophoraceae.
ii) A root-parasite herb containing little or no chlorophyll, e.g., Orobanche caryophylla- cea (Fig. 1.11 B) of Orobanchaceae.
iii) A root-parasite at times becomes stem- parasite with a flower of about 1 metre (3 feet) in diameter, e.g., Rafflesia arnoldi (Fig. 1.11C) of Rafflesiaceae found in the East Indies.
i) A stem-parasite having thread-like twiners, e.g., Dodder, Cuscuta reflexa (Fig. 1.12) of Convolvulaceae.
ii) A stem-parasite having thread-like herb, e.g., Cassytha filiformis of Lauraceae.
iii) A stem-parasite is a smallest angiosperm (dicotyledonous plant), e.g., Arceuthobium minutissimum of Loranthaceae.
2. Partial parasites or semi-parasites or hemi-parasites. Sometimes the parasites may be partially dependent on the hosts as they are capable of producing part of their own food, called partial parasites or semi-parasites or hemi-parasites.
They are of two types:
Sandalwood tree, Santalum album, and Thesium alpinum (Fig. 1.13) of Santalaceae;
Viscum album (Fig. 1.14A), Loranthus longiflorus (Fig. 1.14B) of Loranthaceae; Cassytha filiformis (Fig. 1.14C) of Lauraceae.
These plants obtain their food (organic) entirely from dead plants or animals and decaying organic matters. They draw only the organic food which makes sharp difference with the autophytes and heterophytes.
They are divided into two groups:
1. Total saprophytes or holosaprophytes, and
2. Partial saprophytes.
1. Total saprophytes:
This type is common in bacteria and in fungi. Among higher plants Monotropa uniflora (Fig. 1.15) of Pyrolaceae, a leafless saprophyte lives in moist humus.
Other common examples are Burmannia sp. of Burmanniaceae, Andruris sp. of Triuridaceae, Obolaria sp., Bartonia sp. etc. of Gentianaceae; some orchids like Neottia sp., Corallorhiza sp., Epipogon sp. etc.; prothalli of some ferns like Ophioglossum, Helminthostachys and Botrychium of Ophioglossaceae and many other members among higher plants.
2. Partial saprophytes:
These are green plants which obtain a portion of their nutrition from organic substances, but are not found to utilise it directly. This is done through some fungi living in the roots of higher plants. This type of association is called mycorrhizal association (Fig. 1.16).
(c) Insectivorous or Carnivorous:
These are the plants which grow in localities where the soil is deficient in nitrogen content – essential for normal life. These plants are either with weakly developed root system or are without roots. These plants are also provided with specially modified leaves meant for capturing insects and securing nitrogen from their body.
Some common Indian members are:
(i) The bladderwort, Utricularia stellaris (Fig. 1.17A, B) of Lentibulariaceae – commonly grows in old ponds,
(ii) The pitcher plants, Nepenthes khasiana (Fig. 1.17C, D) of Nepenthaceae, common in some areas of Assam with high humidity,
(iii) The sundew, Drosera burmanii, D. rotunditolia (Fig. 1.18A) and D. indica are found in Birbhum and Bankura districts of West Bengal, Panchmari hills of M.P. etc.
(iv) The venus flytrap, Aldrovanda vesiculosa (Fig. 1.18B-D) of Droseraceae, a submerged plant in salty water, and (v) only one member of Pinguicula, P. alpina (Fig. 1.18E), reported from alpine Himalaya.
Some other members like Cephalotus, Dionaea, Darlingtonia, Heliamphora, Sarracenia etc. are found in other parts of the world, but not in India.
(d) Phagotrophic Plants:
These plants ingest food matters in solid form, e.g., slime moulds.