OCR Specification focus:
‘Describe natural plant clones and explain how to take cuttings as a simple cloning technique in horticulture.’
Natural plant cloning allows identical offspring to arise from a single parent without sexual reproduction, providing a rapid, reliable means of propagation for horticulture and conservation.
Natural Plant Cloning
Many plant species possess a natural capacity for vegetative propagation, where new individuals arise from the vegetative tissues of the parent, such as roots, stems, or leaves. These offspring are clones, meaning they are genetically identical to the parent plant. This form of asexual reproduction is advantageous for maintaining favourable genetic traits across generations and is widely used in horticultural practices.
Clone: An organism or group of cells genetically identical to the original parent organism.
Vegetative propagation relies on the ability of plant cells to dedifferentiate and form meristematic tissue, capable of dividing and generating all other cell types. This property underpins both natural cloning processes and artificial techniques such as taking cuttings or micropropagation.
Natural Plant Clones in Vegetative Propagation
Plants reproduce naturally through a range of vegetative structures that can generate new individuals. Each type provides a mechanism for dispersal and survival, especially in stable environments where genetic uniformity is advantageous.
1. Rhizomes
Rhizomes are underground horizontal stems that grow laterally through the soil. Buds along the rhizome can develop into new shoots, while roots emerge from the underside.
Common in plants such as ginger, bamboo, and irises.
Enable survival through unfavourable conditions by storing nutrients.
Allow rapid colonisation of nearby soil.
2. Stolons or Runners
Stolons (runners) are above-ground horizontal stems that develop from the main shoot. At nodes along the runner, adventitious roots and shoots grow to form independent plants once separated.
Found in species such as strawberries and spider plants.
Facilitate efficient spread across the soil surface.
Offspring remain connected temporarily to the parent, sharing water and nutrients.
New plants can arise naturally from runners (stolons) when nodes contact moist soil and form adventitious roots and plantlets.
Spider plant showing a stolon bearing a plantlet at the node. The plantlet roots and establishes as a clone of the parent, illustrating vegetative propagation by runners. This is directly analogous to runner formation in strawberries. Source
3. Suckers
Suckers are new shoots that arise from the roots of the parent plant, often following damage to the main stem. These shoots can emerge some distance away.
Occur in elm, raspberry, and blackcurrant.
Enable regeneration after disturbance or disease.
Form clonal colonies around the original plant.
4. Bulbs
Bulbs are underground storage organs composed of fleshy leaf bases surrounding a central bud. Each year, the bud grows into a new shoot, while new bulbs (called daughter bulbs) may develop.
Many perennials clone themselves via underground storage organs such as bulbs, corms, rhizomes and tubers.
Labeled longitudinal section of a bulb (onion) showing the basal plate, fleshy leaf scales and developing shoot. Bulbs reproduce vegetatively by forming bulblets, producing clonal offspring. The diagram includes fine anatomical detail appropriate for A-level study. Source
Seen in onions, tulips, and daffodils.
Provide energy reserves for regrowth after dormancy.
Allow multiplication of genetically identical offspring.
5. Corms
Corms are solid, swollen stem bases that store nutrients and survive unfavourable seasons. Each corm can give rise to one or more new corms from buds on its surface.
Typical examples include crocus and gladiolus.
Function similarly to bulbs but are composed of stem tissue rather than leaf bases.
6. Tubers
Tubers are enlarged structures, either stems or roots, that contain stored carbohydrates. Each tuber has eyes or buds capable of sprouting into new plants.
Example: potatoes (stem tubers) and dahlias (root tubers).
Act as energy stores and means of dispersal.
Each bud can develop into an independent clone.
Advantages of Natural Plant Cloning
Natural cloning is common in stable environments where adaptation to new conditions is less critical. Key advantages include:
Genetic consistency: desirable traits such as flower colour or fruit quality are preserved.
Rapid population expansion: allows quick colonisation without pollinators or seed dispersal.
Resilience: established root systems and nutrient stores increase survival chances.
Reproductive assurance: reproduction can occur even in isolation or when environmental factors hinder sexual reproduction.
However, the absence of genetic variation means that a disease or environmental change affecting one clone can potentially devastate all individuals in a population.
Artificial Cloning in Horticulture: Cuttings
Horticulturists utilise the plant’s natural ability to form clones by taking cuttings — small sections of stem, leaf, or root tissue capable of growing into a new plant under suitable conditions.
Cutting: A section of plant tissue taken from a parent plant and grown under controlled conditions to produce a genetically identical clone.
Taking Cuttings: Step-by-Step Technique
Cuttings are one of the simplest and most cost-effective methods of artificial cloning, especially in commercial plant production. The following outlines the general process:
Selection of Material
Choose a healthy, disease-free parent plant with desirable traits.
Select non-flowering shoots to avoid resource diversion from root formation.
Preparation of Cutting
A 4–10 cm stem cutting is typically taken just below a leaf node, using a sharp, sterile blade to reduce infection risk.
Leaves on the lower part of the cutting are removed to reduce transpiration.
Use of Rooting Hormones
The cut end is often dipped in a rooting hormone (e.g. auxin-based powders) to stimulate root growth from the base.
These hormones encourage the development of adventitious roots—roots that form from non-root tissue.
To take a stem cutting, cut just below a node, remove lower leaves, dip the base in rooting hormone, and insert into sterile, well-drained medium.
Demonstration of dipping the prepared cutting base into rooting hormone before insertion into the medium. Rooting compounds increase the rate and uniformity of adventitious root formation. This panel focuses on the hormone step without clutter. Source
Planting Medium
The cutting is inserted into a moist, sterile growing medium, such as perlite, vermiculite, or a mix of compost and sand.
Good aeration and moisture retention are essential for root development.
Environmental Control
Maintain high humidity (e.g. using a propagator or plastic cover) to minimise water loss.
Keep at an optimum temperature and light intensity for photosynthesis.
Avoid waterlogging, which can cause rot.
Root Development and Transplantation
Once new roots have formed, the cutting is transferred to soil for continued growth and development.
After acclimatisation, the young clone behaves as an independent plant.
Types of Cuttings
Different plant species require specific cutting types:
Stem cuttings: roses, geraniums.
Leaf cuttings: begonias, African violets.
Root cuttings: blackberries, horseradish.
Each method exploits the plant’s innate capacity for totipotency—the ability of a single cell to regenerate into a whole organism.
Totipotency: The ability of a single plant cell to divide and differentiate into all types of plant cells, forming an entire organism.
Evaluating the Technique
Taking cuttings is a simple, low-cost and reliable cloning technique, producing genetically uniform offspring without complex equipment. It maintains the favourable traits of the parent and reduces the time to maturity compared with seed-grown plants. However, as with all forms of cloning, the lack of genetic variation means vulnerability to disease and environmental stress remains a key limitation.
FAQ
Temperature, humidity, and light intensity all affect rooting success. Warm temperatures (around 20–25°C) enhance enzyme activity for root growth, while high humidity reduces water loss before roots form.
Indirect light encourages photosynthesis without excessive transpiration. The growing medium must balance moisture retention with aeration — overly wet conditions cause rot, whereas dryness halts root development.
Seasonal factors also matter: spring and early summer provide the best physiological state for active growth and rooting.
Non-flowering shoots devote more energy to vegetative growth, including root formation.
Flowering shoots divert carbohydrates and hormones toward reproduction, reducing the resources available for root initiation. In addition, removing flowers prevents transpiration stress and wilting, both of which can decrease the likelihood of successful establishment.
Therefore, cuttings taken from non-flowering stems root more quickly and reliably than those from flowering ones.
Two main hormones regulate cloning processes: auxins and cytokinins.
Auxins (e.g. indole-3-acetic acid) promote cell elongation and root initiation, especially in the formation of adventitious roots on cuttings.
Cytokinins stimulate shoot growth and cell division, maintaining balance with auxin levels.
In practice, synthetic auxins in rooting powders mimic this natural hormonal control to accelerate root formation and improve cutting survival rates.
No, success varies with species and tissue type. Herbaceous plants (e.g. geraniums, basil) root readily because their tissues are less lignified and regenerate faster.
Woody plants (e.g. roses, conifers) require more precise conditions or softwood/semi-hardwood cuttings and may need hormone treatment. Some species are better propagated by other methods like grafting or tissue culture due to poor rooting ability.
The key factors are plant age, tissue type, and hormonal balance.
Adventitious roots develop from non-root tissues such as stems, leaves, or old woody tissue, rather than from a plant’s root system.
They form in response to injury, hormonal signals, or environmental cues and are vital in both natural cloning (e.g. runners) and artificial propagation (e.g. cuttings).
Unlike normal roots that emerge from the radicle during seed germination, adventitious roots arise from meristematic cells that dedifferentiate, helping plants reproduce and regenerate even when detached from the parent.
Practice Questions
Question 1 (2 marks)
Explain what is meant by a clone in the context of natural plant reproduction.
Mark Scheme:
1 mark for stating that clones are genetically identical individuals or cells.
1 mark for identifying that they are derived from a single parent through asexual reproduction (no fusion of gametes).
Question 2 (5 marks)
Describe how a horticulturist could use stem cuttings to produce clones of a desirable plant. Include the main steps and conditions required for success.
Mark Scheme:
Award up to 5 marks for the following points (maximum 1 mark per point):
Select a healthy, non-flowering shoot from the parent plant.
Cut just below a node using a sharp, sterile blade to prevent infection.
Remove lower leaves to reduce water loss through transpiration.
Dip the cut end in rooting hormone to stimulate adventitious root growth.
Place the cutting in a moist, sterile growing medium (e.g. perlite, compost and sand).
Maintain high humidity (using a propagator or cover) and warm temperature/light for photosynthesis.
Allow roots to develop, then transplant to soil once established.
(Maximum 5 marks — accept equivalent phrasing for horticultural terminology.)
