Undergraduate Honors Thesis Projects

Date of Award


Document Type

Honors Paper

Degree Name

Biochemistry and Molecular Biology-BS


Biology & Earth Science


Dr. Jeffery Lehman

First Committee Member

Dr. John Tansey

Second Committee Member

Dr. Margaret Koehler


Maple, Botany, Toxicosis, Equine, Sapindaceae, Hippocastanoideae

Subject Categories



Maple leaf toxicosis is a lethal condition in which wilted leaves from the plant genus Acer are ingested by equines, leading to hemolytic anemia and methemoglobinemia. In prior studies, the toxicity of various Acer species was quantified, revealing a wide array of responses in terms of hemolysis and methemoglobin production. The object of this study, therefore, is to determine the toxicity of Acer’s closest relatives within the family Sapindaceae, specifically the four additional genera in the subfamily Hippocastanoideae. The information gained from this study will be used to understand the evolution of the toxins responsible for hemolysis and methemoglobin production. The genera used in this study include Aesculus, Dipteronia, Billia and Handeliodendron in addition to Acer. Wilted leaf tissue for each genus was obtained from arboreta, as well as preserved leaf tissue obtained from the National Museum of Natural History of the Smithsonian Institution. Leaf tissue was suspended in buffer and combined with equine erythrocytes in a bioassay that indirectly measured relative amounts of toxin. Percentage hemolysis and percentage methemoglobin production were calculated spectrophotometrically and used to quantify the toxicity of each genus. These tests revealed that extracts of all Acer relatives caused as much hemolysis as did extracts from Acer rubrum. In fact, extracts from Billia, Aesculus, Handeliodendron, and Dipteronia (Arnold) cause numerically higher amounts of hemolysis than did extracts from Acer rubrum. In contrast, only extracts from Billlia hippocastunum and B. rosea caused higher levels of methemoglobin production than did extracts of Acer rubrum. While the amount of methemoglobin production for Dipteronia, Aesculus, and Handeliodendron were less than that for Acer rubrum, these genera still caused numerically higher levels of methemoglobin than did the control. When comparing the results of the hemolysis and methemoglobin formation tests, four groups were established: 1) moderate hemolysis and low methemoglobin production (Dipteronia (Dawes)), 2) high hemolysis and low methemoglobin production (Handeliodendron, Aesculus, and Dipteronia (Arnold)), 3) moderate hemolysis and moderate methemoglobin production (Acer rubrum), and 4) high hemolysis and high methemoglobin production (Billia hippocastunum and rosea). Based on sequence comparisons of locus trnG-trnS, the five genera within Hippocastanoideae cluster into two clades reflecting the traditional taxa of Acereae (Acer and Dipteronia) and Hippocastaneae (Aesculus, Handeliodendron, and Billia). Our results provide strong evidence that the chemical compound that causes hemolysis evolved before the diversification of the two subgroups within Hippocastanoideae. The results for the chemical responsible for methemoglobin were less clear but were consistent with a similar pattern.

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Available for download on Friday, April 24, 2026

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