Internode Morphology in Common Blackberry

INTRODUCTION Observations: Blackberry is common in the Jewel Moore Nature Reserve Blackberry can be an invasive species, just like Japanese Honeysuckle. It seemed to grow more prolifically in the sunlight. Question: Having already studied inter-node length dependency on sunlight in invasive honeysuckle, we wanted to know if this morphological adaptation would be shown in another common invasive species.

INVASIVE SPECIES  Invasive species are especially problematic in areas that have been disturbed by human activities.  Natural disturbances, such as fires, floods, tornadoes, landslides, and tree falls also provide avenues for invasive species to get started.  Some native plants display invasive growth tendencies in their native ranges, often as a response to natural or human-caused disturbances.

CHARACTERISTICS OF COMMON BLACKBERRY  F avors moist to slightly dry prairie edges along woodlands, open woodlands, areas along roadsides and railroads, abandoned pastures, and disturbed, burned-over areas in and around woodlands  Arching or trailing stems, to 3.4 m in height; stems red or green; prickles or bristles usually present; leaves compound, 3-7 serrate leaflets; red or black 'raspberry' fruit; white flowers. (source and  It prefers sunlight, and produces best in full sun, but can tolerate partial shade. However, plants don't grow or produce well in heavy shade.

HYPOTHESES Alternative Hypothesis: The internode length of Rubus allegheniensis will be shorter in the direct sun and longer in the shade. Null Hypothesis: There will be no significant difference in internode length due to varying sun light availability. Shade Sun

METHODS Twenty shoots each were collected from both areas of shade and areas of more prolific sunlight:  Starting at the North edge of the reserve, we walked South (parallel to Ferris Road) three times, moving 20 meters East each time.  Using hand clippers, we retrieved a sample size of 20 individuals from sunny areas and 20 representing shady areas. The internode lengths of sun and shade shoots were measured and recorded in millimeters. The results were run on Systat to determine the mean, standard deviation, and variance between variables.

RESULTS Figure 1. Comparative average internode lengths of blackberry plants in the sun and shade.

RESULTS CONTINUED… Table 1. Statistical results for T-test run on internode length data.

DISCUSSION  The data show a significant difference in the average internode lengths of plants from shade and from sun.  The plants grown in shadier areas had significantly larger internode lengths.  Therefore, the null hypothesis can be rejected – the data supports our functional hypothesis. Greater Shade Sun

DISCUSSION CONTINUED…  The results are indicative of the Optimal Foraging Theory’s presence in Rubus allegheniensis’s growth patterns:  (The optimal foraging theory states that plants and animals attempt to feed in ways that optimize acquisition of energy and nutrients.  In the sun, more leaves were grown to make use of the excess sunlight, causing shorter internodes.  However, in the shade, instead of growing leaves, the plant extended its internode length in an attempt to reach the sunlight that it prefers.

INTERNODE LENGTH AS A MORPHOLOGICAL ADAPTATION Shade Sun

CONCLUSIONS The morphological variation within this species is similar to that of the invasive Lonicera japonica (Honey Suckle). Both species have the ability to be flexible in response to environmental changes. This also reflects optimal foraging theory, and thus flexible change in plants, by showing that plants utilize the resources that are available to them by “changing growth form and resource allocation in response to environmental cues.” ( sources: class notes, A Framework for Plant Behaviors: Jonathan Silvertown; Deborah M. Gordon. Annual Review of Ecology and Systematics, Vol. 20. (1989), pp Stable URL: and text book )

A stream bed that has been cleared of an invasive blackberry species.