Sweetpotato (Ipomoea batatas ) is a member of the morning glory family Convolvulaceae and unlike Irish potatoes (Solanum tuberosum) are not tuber propagated plants. A “tuber” is a short thickened portion of an underground branch derived from an underground stolon and is similar in structure to an aboveground stem. Along a tuber are “eyes” each of which comprises a ridge with a scale-like leaf(like a branch leaf.) This contrasts with sweetpotatoes which produce an edible storage root that is developmentally and anatomically a true root derived from root tissue. Sweetpotatoes do not form tubers.
Historically the dominant sweetpotato variety produced in the United States is ‘Beauregard’ (unpatented). A new distinct sweetpotato variety named ‘Covington’ was developed and patented Feb. 26, 2008 and has been grown extensively as a newer variety for sweetpotato commercial food product. The key very significant difference between the plants of the ‘Mahon Yam’ and ‘Beauregard’ and ‘Covington’ plants is that the ‘Beauregard’ and ‘Covington’ leaves are cordate to triangular in shape with no slight lobing while the ‘Mahon Yam’ leaves are deep lobed. Informal tastings have shown the ‘Mahon Yam’ has excellent flavor, very sweet with excellent mouth feel, and not stringy as compared to many non ‘Mahon Yam’ commercially available sweetpotatoes.
The color of the flesh of sweetpotatoes varies from cultivar to cultivar; varying from white to orange to purple. Presently the dominant sweetpotatoes which are produced are ‘Beauregard’ unpatented and ‘Covington’ patented. This variety ‘Mahon Yam’ has orange flesh, which is superior for its sweetness, moistness and lack of strings (creamy) as determined by informal reviews by many individuals. This variety is also identified by unusual leaves for an eating quality sweetpotato. The leaves normally have seven (7) distinct lobes.    Lineage: Sweetpotatoes are known to mutate, sport, change readily over time. This is one reason for micropropagation; that is, cultivar stability. It is well known that any variety will run out; conversely, selection of the best mutations may result in a greatly improved sweetpotato. The ‘Mahon Yam’ variety resulted from continuous, rigorous selection and reselection from over 25 years for eating quality, productivity and visually appealing shape. ‘Mahon Yam’ originated from a discovery selection of plants grown from storage root derived sprouts from a group of storage roots received from an old farmer in Chesterfield County, S.C. The name of the parent variety is unknown. After some years, the yearly reselection sweetpotatoes were informally compared to the parent variety from the original farm and found to be a darker orange, more attractive, flesh color as well as being sweeter with a smoother mouth feel. The ‘Mahon Yam’ variety was continued to be cultivated to be improved by further election each and every year until being sent to the NCSU Micropropogation Unit. This particular mutation, the ‘Mahon Yam’ is excellent for eating with a unique leaf shape for vegetable sweetpotatoes. The best potatoes were sent to the NCSU Micropropagation Unit in order to eliminate viruses and pathogens via mericulture clean up.    Asexual reproduction: ‘Mahon Yam’ has been asexually propagated via storage roots derived sprouts from continually reselected plants and storage roots since its original selection over twenty-five years ago. Storage and plant selection was done at 310 Third Street, Cheraw, S.C. Each year the most productive, best tasting were selected and the storage roots were separately stored for the next years trials at this location.
The “on farm” trial was conducted at two (2) locations near Cheraw, S.C. from vegetatively, asexually reproduced storage root derived sprouts from stock used for micropropagation. The production was stable, excellent in all respects even during a time of intense drought. Asexual propagation of this new cultivar by cutting and sprouts are stable and the plant produces true to type in successive generations of asexual propagation.