There are many different offerings for the ancestry of Aelfgar, Earl of Mercia, whose daughters, confirmed and alleged, appear in many ancestries. The following pulls together the position as we see it but is not completely secure. We find that many online genealogical databases show dates that are simply not acceptable and this, along with a failure to identify sources, weakens faith in them.

The following connections are shown here for the moment (at least) whilst Ivo Taillebois is investigated further. His ancestry appears to be one of the most inconsistently reported on the Internet. Not helped by the confusion over the identity of his wife Lucy, as mentioned just above, he is variously described as:
(1) brother (possibly illegitimate) of a Count of Anjou. This is probably the most common description (which is supported by BE1883 in its article on the Lancaster family). Where the Count is named, most sources give his name as Fulk - normally (as in BE1883) without specifying which Fulk but sometimes specifying one whose dates are obviously incompatible. The only Fulks (indeed the only Counts of Anjou) whose dates would reasonably work for Ivo appear to be Fulk III 'the Black' (c956-1040), but only if he was illegitimate, and possibly (given the uncertainty on Ivo's dates) Fulk IV 'le Rechin' (1043-1109). An interesting variation to this theme is that he was not a son but a grandson of a Count of Anjou, being grandson of Fulk III 'the Black' through his daughter Adele, by Bodon (Eudes) de Nevers.
(2) an illegitimate son of Richard III, Duke of Normandy.
(3) son of an unidentified Richard FitzGerold. Some of the sources that report this give Ivo a family name of FitzRichard de Roumare. This is questionable because it appears to assume a connection with Roger FitzGerold of Roumare even though that Roger was of the same generation as Ivo (as shown by the fact that Roger married Ivo's widow, Lucy - see above) and so any descent from a Gerold of Roumare would be very unlikely to be through an intervening generation (Richard).
(4) "nephew of the Conqueror".
(5) a son (possibly illegitimate) of either Gilbert (Gislebert), Count of Brienne (1000-1040) or Gilbert Crispin de Bec, who are frequently confused with each other. The former would make Ivo a second cousin of the Conqueror. The latter seems unlikely because Ivo's wife Lucy appears to have been Gilbert Crispin's great-granddaughter as Gilbert's daughter Hesilia married William (or Robert) Malet, apparently the father of Lucy's uncle Robert of Eye (see note under Lucy on 'Malet1') as well as possibly father of Lucy's mother (Beatrice?).

Confirmation of the identity of Ivo's children is still being sought. Some web sites show him as having a daughter Lucy but this appears not to be true (see comment on 'Malet1'). At least one web site states that he died without issue and that his title and estates went to a brother called Gerard. However, the general consensus is that he did have surviving children who themselves had children. One of the uncertainties concerning his children is that, whilst many sites report him as father of Eldred (ancestor of the family of Lancaster) and some show him as father of Aelfred (ancestor of the family of Radcliffe), very few show both at the same time.