Short answer. Share and share alike — half each. Where property is donated or left by will to both spouses without designation of determinate shares, the law divides it equally. Each half is the receiving spouse's own exclusive property, not part of the marital pool.
What the law says
Property donated or left by will to the spouses, jointly and with designation of determinate shares, shall pertain to the donee-spouses as his or her own exclusive property, and in the absence of designation, share and share alike
Family Code, Article 113 — Property Donated or Left Jointly to the Spouses. Read the full provision →
The default is equality, not the marital regime
Two things are settled at once. Silence about proportions does not make the gift void for uncertainty, and it does not throw the property into the community either — the law simply reads the shares as equal. Where the instrument does name determinate shares, those shares govern, which is why a donor who wants something other than a half each must say so on the face of the document. Notice how narrow the rule is: it applies to property given or bequeathed to the spouses, jointly. A gift to one spouse alone is not within it at all.
Each share is exclusive property
The more consequential word is exclusive. What each spouse receives pertains to that spouse as his or her own property, not to the couple jointly and not to whatever regime governs your marriage. So your half is yours to own, possess and administer, and it is answerable for the marriage's obligations only to the extent the law makes exclusive property answerable. Spouses who assume that anything received during the marriage is automatically shared get this backwards. Here the sharing is between the two of you as separate owners, each of whom happens to own half.
Co-ownership of a single lot has practical consequences
Owning a lot in equal but undivided halves is not the same as owning half a lot. Until the property is partitioned, neither of you owns any identified portion of the ground, which is what makes selling, mortgaging or building on it awkward without the other's participation. The equal shares the law supplies tell you the size of each interest, not where it lies. If the two of you want a clean line on the ground, that is a partition, and it is a separate step from receiving the gift.
Accretion, and what to read first
The article preserves the right of accretion when proper, the mechanism by which a share that fails — because a donee predeceases the testator, for instance — goes to the other rather than falling outside the gift. Whether it operates depends on how the instrument is worded. So the document is where to begin: get the deed of donation or the will and read it for the exact description of the donees, any statement of proportions, any condition attached, and its date. A lawyer will want that instrument before anything else you can bring.